<PAGE>


           As filed with the Securities and Exchange Commission on April 6, 2000
                                                Registration No. 333-___________

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                                Washington, D.C.

                       ---------------------------------

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                        ---------------------------------

                         NORTH AMERICAN SCIENTIFIC, INC.
             (Exact name of registrant as specified in its charter)

                DELAWARE                                         51-0366422
     (State or other jurisdiction of                         (I.R.S. Employer
      incorporation or organization)                        Identification No.)

  20200 SUNBURST STREET, CHATSWORTH, CA                            91311
(Address of Principal Executive Offices)                        (Zip Code)

                        2000 EMPLOYEE STOCK PURCHASE PLAN
                            (Full title of the plan)

                                L. MICHAEL CUTRER
                         NORTH AMERICAN SCIENTIFIC, INC.
                              20200 SUNBURST STREET
                          CHATSWORTH, CALIFORNIA 91311
                     (Name and address of agent for service)

                                 (818) 734-8600
          (Telephone number, including area code, of agent for service)

                         CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------
                                                           Proposed          Proposed
         Title of                Amount                    maximum           maximum          Amount of
         securities to           to be                     offering price    aggregate        registration
         be registered           registered                per share         offering price   fee
------------------------------------------------------------------------------------------------------------
<S>                              <C>                       <C>               <C>              <C>
         Common Stock,
         $0.01 par value         300,000 shares (a)        $14.6893 (b)      $4,406,790 (b)   $1,368.69 (c)

------------------------------------------------------------------------------------------------------------
</TABLE>

(a)  Represents the maximum number of shares which could be purchased upon
     exercise of all options which may be hereafter granted under the provisions
     of the 2000 Employee Stock Purchase Plan.
(b)  Estimated in accordance with Rule 457(h)(1) under the Securities Act, based
     on 85% of the average of the high and low prices of the Common Stock
     reported on April 5, 2000 on the Nasdaq National Market.
(c)  Registration Fee computed pursuant to Rule 457(h)(1).


<PAGE>


                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT


ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

     The documents listed in (a) through (c) below are incorporated by reference
in this Registration Statement, and all documents subsequently filed by North
American Scientific, Inc. (the "Company") pursuant to Sections 13(a), 13(c), 14
and 15(d) of the Securities Exchange Act of 1934, prior to the filing of a
post-effective amendment which indicates that all securities offered have been
sold or which deregisters all securities then remaining unsold, shall be deemed
to be incorporated by reference in this Registration Statement and to be part
thereof from the date of filing of such documents:

     (a)  The Company's annual report on Form 10-K for the year ended October
          31, 1999.

     (b)  The Company's quarterly report on Form 10-Q for the quarter ended
          January 31, 2000.

     (c)  The description of the Company's Common Stock which is contained in
          the Registration Statement on Form 10-SB filed August 22, 1995, File
          No. 0-26670, including any amendment or report filed for the purpose
          of updating such description.

ITEM 4.  DESCRIPTION OF SECURITIES.

     Not Applicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

     The validity of the shares of Common Stock offered hereby will be passed
upon by D'Ancona & Pflaum LLC, Chicago, Illinois. Mr. Allan J. Reich, a managing
member of D'Ancona & Pflaum LLC, beneficially owns 58,250 shares of the
Company's Common Stock. Other members of D'Ancona & Pflaum LLC beneficially own
additional shares of the Company's Common Stock, which ownership is not
material.


<PAGE>


ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

     The Delaware General Corporation Law (the "DGCL") permits a corporation to
indemnify officers, directors, employees and agents for actions taken in good
faith and in a manner they reasonably believed to be in, or not opposed to, the
best interests of the corporation, and with respect to any criminal action,
which they had no reasonable cause to believe was unlawful. The DGCL provides
that a corporation may advance expenses of defense (upon receipt of a written
undertaking to reimburse the corporation if indemnification is not appropriate)
and must reimburse a successful defendant for expenses, including attorney's
fees, actually and reasonably incurred, and permits a corporation to purchase
and maintain liability insurance for its directors and officers. The DGCL
provides that indemnification may not be made for any claim, issue or matters as
to which a person has been adjudged by a court of competent jurisdiction, after
exhaustion of all appeals therefrom, to be liable to the corporation, unless and
only to the extent a court determines that the person is entitled to indemnity
for such expenses as the court deems proper.

     The Certificate of Incorporation of the Company (the "Certificate")
provides that each person who is involved in any actual or threatened action,
suit or proceeding, whether civil, criminal, administrative or investigative, by
reason of the fact that he or she is or was a director of the Company, or is or
was serving at the request of the Company as a director of another corporation
or of a partnership, joint venture, trust, or other enterprise, will be
indemnified by the Company, and that each person who is so involved by reason of
the fact that he or she was an officer, agent of the Company, or is or was
serving at the request of the Company as an officer, agent or employee of
another corporation, or of a partnership, joint venture, trust or other
enterprise, may be indemnified by the Company in accordance with the DGCL. The
indemnification rights conferred by the Certificate are not exclusive of any
other right to which persons seeking indemnification may be entitled under any
law, bylaw, agreement, vote of stockholders or disinterested directors or
otherwise. The Company has purchased and maintains insurance on behalf of its
directors, officers, employees and agents.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

     Not Applicable.

ITEM 8.  EXHIBITS.

     4.1  Certificate of Incorporation of the Corporation, incorporated by
          reference to Exhibit 3(i) of the Company's Registration Statement on
          Form 10-SB, filed August 22, 1995.

     4.2  Certificate of Amendment to Certificate of Incorporation of the
          Company, incorporated by reference to Exhibit 3.1 of the Company's
          quarterly report on Form 10-QSB for the fiscal quarter ended July 31,
          1998.

     4.3  Bylaws of the Company, as amended, incorporated by reference to
          Exhibit 3(ii) the Company's Registration Statement on Form S-8, filed
          October 18, 1996.

     4.4  The North American Scientific, Inc. 2000 Employee Stock Purchase Plan.

     5.1  Opinion of D'Ancona & Pflaum LLC.

     23.1 Consent of PricewaterhouseCoopers LLP.

     23.2 Consent of D'Ancona & Pflaum LLC (included in Exhibit 5.1).


<PAGE>


        24.1    Power of Attorney (included herein on the signature page).

ITEM 9.  UNDERTAKINGS.

        The Company hereby undertakes:

        (1)     To file, during any period in which offers or sales are being
                made, a post-effective amendment to this registration statement:

                (i)     To include any prospectus required by section 10(a)(3)
                        of the Securities Act of 1933;

                (ii)    To reflect in the prospectus any facts or events arising
                        after the effective date of the registration statement
                        (or the most recent post-effective amendment thereof)
                        which, individually or in the aggregate, represent a
                        fundamental change in the information set forth in the
                        registration statement;

                (iii)   To include any material information with respect to the
                        plan of distribution not previously disclosed in the
                        registration statement or any material change to such
                        information in the registration statement;

                PROVIDED, HOWEVER, that paragraphs (1)(i) and 1(ii) do not apply
                if the registration statement is on Form S-3, Form S-8 or Form
                F-3 and the information required to be included in a
                post-effective amendment by those paragraphs is contained in
                periodic reports filed by the registrant pursuant to section 13
                or section 15(d) of the Securities Exchange Act of 1934 that are
                incorporated by reference in the registration statement.

        (2)     That, for the purpose of determining any liability under the
                Securities Act of 1933, each such post-effective amendment shall
                be deemed to be a new registration statement relating to the
                securities offered therein, and the offering of such securities
                at that time shall be deemed to be the initial bona fide
                offering thereof.

        (3)     To remove from registration by means of a post-effective
                amendment any of the securities being registered which remain
                unsold at the termination of the offering.

        The Company hereby undertakes that, for the purposes of determining any
liability under the Securities Act of 1933, each filing of the Company's annual
report pursuant to section 13(a) or section 15(d) of the Securities Exchange Act
of 1934 that is incorporated by reference in the Registration Statement shall be
deemed to be a new registration statement relating to the securities offered
therein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.

        Insofar as indemnification for liabilities arising under the Securities
Act of 1933 may be permitted to directors, officers and controlling persons of
the Company, the Company has been advised that in the opinion of the Securities
and Exchange Commission such indemnification is against public policy as
expressed in the Act and is, therefore, unenforceable. In the event that a claim
for indemnification against such liabilities (other than the payment by the
Company of expenses incurred or paid by a director, officer or controlling
person of the Company in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Company will, unless in the
opinion of its counsel the matter has been


<PAGE>


settled by controlling precedent, submit to a court of appropriate jurisdiction
the question whether such indemnification by it is against public policy as
expressed in the Act and will be governed by the final adjudication of such
issue.


<PAGE>


                                   SIGNATURES

     THE REGISTRANT. Pursuant to the requirements of the Securities Act of 1933,
the Registrant certifies that it has reasonable grounds to believe that it meets
all the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Chatsworth, State of California, on the 6th day
of April, 2000.


                                  NORTH AMERICAN SCIENTIFIC, INC.
                                  (Registrant)



                                  By: /s/ L. Michael Cutrer
                                     -------------------------
                                  L. Michael Cutrer, President
                                  and Chief Executive Officer

     The undersigned directors and officers of North American Scientific, Inc.,
a Delaware corporation, which is filing a Registration Statement on Form S-8
with the Securities and Exchange Commission, under the provisions of the
Securities Act of 1933, as amended, hereby constitute and appoint L. Michael
Cutrer their true and lawful attorney-in-fact and agent, with full power of
substitution and re-substitution, for him or her and in his or her name, place
and stead, in any and all capacities, to sign any or all pre-effective and
post-effective amendments to the Registration Statement, and all other documents
in connection therewith to be filed with the Securities and Exchange Commission,
granting unto said attorney-in-fact and agent full power and authority to do and
perform each and every act and thing requisite and necessary to be done in and
about the premises, as fully to all interests and purposes as each of them might
or could do in person, hereby ratifying and confirming all that said
attorney-in-fact and agent or his substitutes, may lawfully do or cause to be
done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.

<TABLE>
<CAPTION>
Signature                                        Title                           Date
---------                                        -----                           ----
<S>                                        <C>                                   <C>
/s/ Irwin J. Gruverman                     Chairman of the Board                 April 6, 2000
------------------------------------       and Director
Irwin J. Gruverman


/s/ L. Michael Cutrer                      President, Chief                      April 6, 2000
------------------------------------       Executive Officer
L. Michael Cutrer                          and Director (Principal
                                           Executive Officer)

/s/ Alan I. Edrick                         Chief Financial Officer               April 6, 2000
------------------------------------       and Chief Accounting Officer
Alan I. Edrick
</TABLE>


<PAGE>


<TABLE>
<S>                                        <C>                                   <C>
/s/ Dr. Allan M. Green                     Director                              April 6, 2000
------------------------------------
Dr. Allan M. Green


/s/ Michael C. Lee                         Director                              April 6, 2000
------------------------------------
Michael C. Lee


/s/ Larry Berkin                           Director                              April 6, 2000
------------------------------------
Larry Berkin
</TABLE>
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 15863}]
{"company-data": {"conformed-name": "NORTH AMERICAN SCIENTIFIC INC", "cik": "0000949876", "assigned-sic": "2835", "irs-number": "954283918", "state-of-incorporation": "DE", "fiscal-year-end": "1031"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-34200", "film-number": "595166"}, "business-address": {"street1": "20200 SUNBURST ST", "city": "CHATSWORTH", "state": "CA", "zip": "91311", "phone": "8187348600"}, "mail-address": {"street1": "20200 SUNBURST ST", "city": "CHATSWORTH", "state": "CA", "zip": "91311"}}
As filed with the Securities and Exchange Commission on April 6, 2000
                                                Registration No. 333-___________

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                                Washington, D.C.

                       ---------------------------------

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                        ---------------------------------

                         NORTH AMERICAN SCIENTIFIC, INC.
             (Exact name of registrant as specified in its charter)

                DELAWARE                                         51-0366422
     (State or other jurisdiction of                         (I.R.S. Employer
      incorporation or organization)                        Identification No.)

  20200 SUNBURST STREET, CHATSWORTH, CA                            91311
(Address of Principal Executive Offices)                        (Zip Code)

                        2000 EMPLOYEE STOCK PURCHASE PLAN
                            (Full title of the plan)

                                L. MICHAEL CUTRER
                         NORTH AMERICAN SCIENTIFIC, INC.
                              20200 SUNBURST STREET
                          CHATSWORTH, CALIFORNIA 91311
                     (Name and address of agent for service)

                                 (818) 734-8600
          (Telephone number, including area code, of agent for service)

                         CALCULATION OF REGISTRATION FEE
------------------------------------------------------------------------------------------------------------
                                                           Proposed          Proposed
         Title of                Amount                    maximum           maximum          Amount of
         securities to           to be                     offering price    aggregate        registration
         be registered           registered                per share         offering price   fee
------------------------------------------------------------------------------------------------------------
Common Stock,
         $0.01 par value         300,000 shares (a)        $14.6893 (b)      $4,406,790 (b)   $1,368.69 (c)

------------------------------------------------------------------------------------------------------------
(a)  Represents the maximum number of shares which could be purchased upon
     exercise of all options which may be hereafter granted under the provisions
     of the 2000 Employee Stock Purchase Plan.
(b)  Estimated in accordance with Rule 457(h)(1) under the Securities Act, based
     on 85% of the average of the high and low prices of the Common Stock
     reported on April 5, 2000 on the Nasdaq National Market.
(c)  Registration Fee computed pursuant to Rule 457(h)(1).
PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

     The documents listed in (a) through (c) below are incorporated by reference
in this Registration Statement, and all documents subsequently filed by North
American Scientific, Inc. (the "Company") pursuant to Sections 13(a), 13(c), 14
and 15(d) of the Securities Exchange Act of 1934, prior to the filing of a
post-effective amendment which indicates that all securities offered have been
sold or which deregisters all securities then remaining unsold, shall be deemed
to be incorporated by reference in this Registration Statement and to be part
thereof from the date of filing of such documents:

     (a)  The Company's annual report on Form 10-K for the year ended October
          31, 1999.

     (b)  The Company's quarterly report on Form 10-Q for the quarter ended
          January 31, 2000.

     (c)  The description of the Company's Common Stock which is contained in
          the Registration Statement on Form 10-SB filed August 22, 1995, File
          No. 0-26670, including any amendment or report filed for the purpose
          of updating such description.

ITEM 4.  DESCRIPTION OF SECURITIES.

     Not Applicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

     The validity of the shares of Common Stock offered hereby will be passed
upon by D'Ancona & Pflaum LLC, Chicago, Illinois. Mr. Allan J. Reich, a managing
member of D'Ancona & Pflaum LLC, beneficially owns 58,250 shares of the
Company's Common Stock. Other members of D'Ancona & Pflaum LLC beneficially own
additional shares of the Company's Common Stock, which ownership is not
material.
ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

     The Delaware General Corporation Law (the "DGCL") permits a corporation to
indemnify officers, directors, employees and agents for actions taken in good
faith and in a manner they reasonably believed to be in, or not opposed to, the
best interests of the corporation, and with respect to any criminal action,
which they had no reasonable cause to believe was unlawful. The DGCL provides
that a corporation may advance expenses of defense (upon receipt of a written
undertaking to reimburse the corporation if indemnification is not appropriate)
and must reimburse a successful defendant for expenses, including attorney's
fees, actually and reasonably incurred, and permits a corporation to purchase
and maintain liability insurance for its directors and officers. The DGCL
provides that indemnification may not be made for any claim, issue or matters as
to which a person has been adjudged by a court of competent jurisdiction, after
exhaustion of all appeals therefrom, to be liable to the corporation, unless and
only to the extent a court determines that the person is entitled to indemnity
for such expenses as the court deems proper.

     The Certificate of Incorporation of the Company (the "Certificate")
provides that each person who is involved in any actual or threatened action,
suit or proceeding, whether civil, criminal, administrative or investigative, by
reason of the fact that he or she is or was a director of the Company, or is or
was serving at the request of the Company as a director of another corporation
or of a partnership, joint venture, trust, or other enterprise, will be
indemnified by the Company, and that each person who is so involved by reason of
the fact that he or she was an officer, agent of the Company, or is or was
serving at the request of the Company as an officer, agent or employee of
another corporation, or of a partnership, joint venture, trust or other
enterprise, may be indemnified by the Company in accordance with the DGCL. The
indemnification rights conferred by the Certificate are not exclusive of any
other right to which persons seeking indemnification may be entitled under any
law, bylaw, agreement, vote of stockholders or disinterested directors or
otherwise. The Company has purchased and maintains insurance on behalf of its
directors, officers, employees and agents.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

     Not Applicable.

ITEM 8.  EXHIBITS.

     4.1  Certificate of Incorporation of the Corporation, incorporated by
          reference to Exhibit 3(i) of the Company's Registration Statement on
          Form 10-SB, filed August 22, 1995.

     4.2  Certificate of Amendment to Certificate of Incorporation of the
          Company, incorporated by reference to Exhibit 3.1 of the Company's
          quarterly report on Form 10-QSB for the fiscal quarter ended July 31,
          1998.

     4.3  Bylaws of the Company, as amended, incorporated by reference to
          Exhibit 3(ii) the Company's Registration Statement on Form S-8, filed
          October 18, 1996.

     4.4  The North American Scientific, Inc. 2000 Employee Stock Purchase Plan.

     5.1  Opinion of D'Ancona & Pflaum LLC.

     23.1 Consent of PricewaterhouseCoopers LLP.

     23.2 Consent of D'Ancona & Pflaum LLC (included in Exhibit 5.1).
24.1    Power of Attorney (included herein on the signature page).

ITEM 9.  UNDERTAKINGS.

        The Company hereby undertakes:

        (1)     To file, during any period in which offers or sales are being
                made, a post-effective amendment to this registration statement:

                (i)     To include any prospectus required by section 10(a)(3)
                        of the Securities Act of 1933;

                (ii)    To reflect in the prospectus any facts or events arising
                        after the effective date of the registration statement
                        (or the most recent post-effective amendment thereof)
                        which, individually or in the aggregate, represent a
                        fundamental change in the information set forth in the
                        registration statement;

                (iii)   To include any material information with respect to the
                        plan of distribution not previously disclosed in the
                        registration statement or any material change to such
                        information in the registration statement;

                PROVIDED, HOWEVER, that paragraphs (1)(i) and 1(ii) do not apply
                if the registration statement is on Form S-3, Form S-8 or Form
                F-3 and the information required to be included in a
                post-effective amendment by those paragraphs is contained in
                periodic reports filed by the registrant pursuant to section 13
                or section 15(d) of the Securities Exchange Act of 1934 that are
                incorporated by reference in the registration statement.

        (2)     That, for the purpose of determining any liability under the
                Securities Act of 1933, each such post-effective amendment shall
                be deemed to be a new registration statement relating to the
                securities offered therein, and the offering of such securities
                at that time shall be deemed to be the initial bona fide
                offering thereof.

        (3)     To remove from registration by means of a post-effective
                amendment any of the securities being registered which remain
                unsold at the termination of the offering.

        The Company hereby undertakes that, for the purposes of determining any
liability under the Securities Act of 1933, each filing of the Company's annual
report pursuant to section 13(a) or section 15(d) of the Securities Exchange Act
of 1934 that is incorporated by reference in the Registration Statement shall be
deemed to be a new registration statement relating to the securities offered
therein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.

        Insofar as indemnification for liabilities arising under the Securities
Act of 1933 may be permitted to directors, officers and controlling persons of
the Company, the Company has been advised that in the opinion of the Securities
and Exchange Commission such indemnification is against public policy as
expressed in the Act and is, therefore, unenforceable. In the event that a claim
for indemnification against such liabilities (other than the payment by the
Company of expenses incurred or paid by a director, officer or controlling
person of the Company in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Company will, unless in the
opinion of its counsel the matter has been
settled by controlling precedent, submit to a court of appropriate jurisdiction
the question whether such indemnification by it is against public policy as
expressed in the Act and will be governed by the final adjudication of such
issue.
SIGNATURES

     THE REGISTRANT. Pursuant to the requirements of the Securities Act of 1933,
the Registrant certifies that it has reasonable grounds to believe that it meets
all the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Chatsworth, State of California, on the 6th day
of April, 2000.

                                  NORTH AMERICAN SCIENTIFIC, INC.
                                  (Registrant)

                                  By: /s/ L. Michael Cutrer
                                     -------------------------
                                  L. Michael Cutrer, President
                                  and Chief Executive Officer

     The undersigned directors and officers of North American Scientific, Inc.,
a Delaware corporation, which is filing a Registration Statement on Form S-8
with the Securities and Exchange Commission, under the provisions of the
Securities Act of 1933, as amended, hereby constitute and appoint L. Michael
Cutrer their true and lawful attorney-in-fact and agent, with full power of
substitution and re-substitution, for him or her and in his or her name, place
and stead, in any and all capacities, to sign any or all pre-effective and
post-effective amendments to the Registration Statement, and all other documents
in connection therewith to be filed with the Securities and Exchange Commission,
granting unto said attorney-in-fact and agent full power and authority to do and
perform each and every act and thing requisite and necessary to be done in and
about the premises, as fully to all interests and purposes as each of them might
or could do in person, hereby ratifying and confirming all that said
attorney-in-fact and agent or his substitutes, may lawfully do or cause to be
done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated.
Signature                                        Title                           Date
---------                                        -----                           ----
/s/ Irwin J. Gruverman                     Chairman of the Board                 April 6, 2000
------------------------------------       and Director
Irwin J. Gruverman

/s/ L. Michael Cutrer                      President, Chief                      April 6, 2000
------------------------------------       Executive Officer
L. Michael Cutrer                          and Director (Principal
                                           Executive Officer)

/s/ Alan I. Edrick                         Chief Financial Officer               April 6, 2000
------------------------------------       and Chief Accounting Officer
Alan I. Edrick
/s/ Dr. Allan M. Green                     Director                              April 6, 2000
------------------------------------
Dr. Allan M. Green

/s/ Michael C. Lee                         Director                              April 6, 2000
------------------------------------
Michael C. Lee

/s/ Larry Berkin                           Director                              April 6, 2000
------------------------------------
Larry Berkin