<PAGE>
 
     As filed with the Securities and Exchange Commission on July 17, 1998

                                                     Registration No. [________]

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


                       SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C.  20549
                              ____________________

                                    FORM S-8

                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933


                               CYTYC CORPORATION
        --------------------------------------------------------------
            (Exact Name of Registrant as Specified in Its Charter)

                   Delaware                                    02-0407755
---------------------------------                      -------------------------
(State or other jurisdiction of                             (I.R.S. Employer
incorporation or organization)                              Identification No.)


                    85 Swanson Road, Boxborough, MA  01719
             -----------------------------------------------------
              (Address of Principal Executive Offices) (Zip Code)
                            _______________________

                                1995 STOCK PLAN
                      ----------------------------------
                           (FULL TITLE OF THE PLAN)
                          __________________________

                              PATRICK J. SULLIVAN
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                               CYTYC CORPORATION
                                85 SWANSON ROAD
                             BOXBOROUGH, MA  01719
                                  (508) 263-8000
                         -----------------------------------------
                      (NAME, ADDRESS AND TELEPHONE NUMBER,
                   INCLUDING AREA CODE, OF AGENT FOR SERVICE)
                              ___________________

                                    COPY TO:

                           JONATHAN M. MOULTON, ESQ.
                        TESTA, HURWITZ & THIBEAULT, LLP
                               HIGH STREET TOWER
                                125 HIGH STREET
                          BOSTON, MASSACHUSETTS 02110
                                 (617) 248-7000
                               
================================================================================

                        CALCULATION OF REGISTRATION FEE

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

<TABLE>
<CAPTION>
                                                         Proposed                Proposed
        Title Of                                          Maximum                Maximum
       Securities                  Amount                Offering               Aggregate            Amount of
          To Be                    To Be                 Price Per               Offering          Registration
       Registered              Registered(1)             Share(2)                 Price                 Fee
-----------------------------------------------------------------------------------------------------------------
<S>                        <C>                     <C>                    <C>                     <C>
 
1995 STOCK PLAN
Common Stock,
$.01 par value                  454,115 shares                $18.00               $8,174,070           $2,411.35

=================================================================================================================
</TABLE>
(1) Pursuant to the terms of the Company's 1995 Stock Plan, an additional
    454,115 shares of Common Stock may be issued effective as of the first
    trading day of 1998 and such additional shares are registered hereby. Upon
    the filing and effectiveness of this Registration Statement on Form S-8, the
    total number of shares of Common Stock registered pursuant to the 1995 Stock
    Plan will be 1,625,615 shares.

(2) None of such shares are subject to outstanding options. The price of $18.00
    per share, which is the average of the high and low prices reported on the
    Nasdaq National Market on July 14, 1998, is set forth solely for
    purposes of calculating the filing fee pursuant to Rule 457(c).

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

   This Registration Statement registers additional securities of the same class
as other securities for which the Registration Statement on Form S-8 (File No.
333-2196), as filed with the Securities and Exchange Commission (the
"Commission") on March 8, 1996 relating to Cytyc Corporation's 1995 Stock Plan, 
and as amended on Form S-8 (File No. 333-22675), as filed with the Commission on
March 3, 1997, is effective. Pursuant to General Instruction E to Form S-8, the
contents of the above-listed Registration Statements are hereby incorporated by
reference.

                                       1
<PAGE>
 
                                    PART II
               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.    Incorporation of Documents by Reference.
           --------------------------------------- 

   The Company previously registered under the Securities Act an aggregate of
1,171,500 shares of Common Stock offered pursuant to the 1995 Stock Plan
pursuant to a Registration Statement on Form S-8 (File No. 333-2196) filed with
the Commission on March 8, 1996, as amended on Form S-8 (File No. 333-22675),
filed with the Commission on March 3, 1997, which are incorporated in this
Registration Statement by reference.

   The following documents filed with the Commission are incorporated by
reference in this Registration Statement:

    (a)  Registrant's Annual Report on Form 10-K for the fiscal year ended
         December 31, 1997 filed pursuant to the Securities Exchange Act of
         1934, as amended (the "Exchange Act");

    (b)  Registrant's Quarterly Report on Form 10-Q for the fiscal quarter ended
         March 31, 1998 filed pursuant to the Exchange Act; and

    (c)  The section entitled "Description of Registrant's Securities to be
         Registered" contained in the Registrant's Registration Statement on
         Form 8-A, filed with the Commission pursuant to Section 12(g) of the
         Exchange Act on January 16, 1996.

    All documents subsequently filed with the Commission by the Registrant
pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act after the
date hereof and prior to the filing of a post-effective amendment which
indicates that all securities offered herein 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 a part hereof from the date
of filing of such documents.

    Any statement contained in any document incorporated, or deemed to be
incorporated, by reference herein shall be deemed to be modified or superseded
for purposes of this Registration Statement to the extent that a statement
contained herein or in any subsequently filed document which also is, or is
deemed to be, incorporated by reference herein modifies or supersedes such
statement.  Except as so modified or superseded, such statement shall not be
deemed to constitute a part of this Registration Statement.

                                       2
<PAGE>
 
Item 8.  Exhibits
         --------

Exhibit No.         Description of Exhibit
-----------         ----------------------

    4(1)            1995 Stock Plan, as amended.

    5(2)            Opinion of Testa, Hurwitz & Thibeault, LLP.
 
    23.1(2)         Consent of Arthur Andersen LLP.

    23.2(2)         Consent of Testa, Hurwitz & Thibeault, LLP (included in
                    Exhibit 5).

    24(3)(4)        Power of Attorney (included as part of the signature page
                    to this Registration Statement).

-----------
(1)  Incorporated by reference to the Company's Registration Statement on 
     Form S-8 (File No. 333-2196), as amended on Form S-8 (File No. 333-22675).

(2)  Filed herewith. 

(3)  Incorporated by reference to page 8 of the Company's Registration Statement
     on Form S-8 (File No. 333-2196).  

(4)  See page 4 hereof.  

                                       3
<PAGE>
 
                                   SIGNATURES

   Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of 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 Boxborough, Commonwealth of Massachusetts, on this
17th day of July, 1998.

                               CYTYC CORPORATION


                               By:     /s/ Patrick J. Sullivan
                                   ---------------------------
                                   Patrick J. Sullivan
                                   President and Chief Executive Officer

                       POWER OF ATTORNEY AND SIGNATURES

   We, the undersigned officers and directors of Cytyc Corporation, hereby 
severally constitute and appoint Patrick J. Sullivan and Joseph W. Kelly, and 
each of them singly, our true and lawful attorneys, with full power to them and 
each of them singly, to sign for us in our names in the capacities indicated 
below, all pre-effective and post-effective amendments to this registration 
statement, and generally to do all things in our names and on our behalf in such
capacities to enable Cytyc Corporation to comply with the provisions of the 
Securities Act of 1933, as amended, and all requirements of the Securities and 
Exchange Commission.  

   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
date indicated.


Signature               Capacity                           Date
---------               --------                           ----

       *                President, Chief Executive     July 17, 1998
-------------------     Officer and Director         
Patrick J. Sullivan     (Principal Executive Officer)
                        


       *                Vice President,                July 17, 1998
-------------------     Chief Financial Officer and    
Joseph W. Kelly         Treasurer                    
                        (Principal Financial and     
                        Accounting Officer)           
                        


/s/ Sally W. Crawford   Director                       July 17, 1998
--------------------- 
Sally W. Crawford


       *                Director                       July 17, 1998
---------------------     
Franklin J. Iris


/s/ William G. Little   Director                       July 17, 1998
--------------------- 
William G. Little


       *                Director                       July 17, 1998
---------------------   
C. William McDaniel


/s/ Anna S. Richo       Director                       July 17, 1998
---------------------                                  
Anna S. Richo


       *                Director                       July 17, 1998
---------------------                           
Monroe Trout, M.D.



*By:  /s/ Patrick J. Sullivan
      -----------------------
      Patrick J. Sullivan
      Attorney-in-Fact

                                       4
<PAGE>
 
                                 EXHIBIT INDEX
                                 -------------
                                        
Exhibit       Description of Exhibit                                    Page No.
-------       ----------------------                                    --------
    4(1)      1995 Stock Plan                                               
 
    5(2)      Opinion of Testa, Hurwitz & Thibeault, LLP                    6
 
    23.1(2)   Consent of Arthur Andersen LLP                                7
 
    23.2(2)   Consent of Testa, Hurwitz & Thibeault, LLP (included in       6
              Exhibit 5)

    24(3)(4)  Power of Attorney (included as part of the signature          4
              page to this Registration Statement).  

-------
(1)  Incorporated by reference to the Company's Registration Statement on 
     Form S-8 (File No. 333-2196) as amended on Form S-8 (File No. 333-22675).

(2)  Filed herewith.  

(3)  Incorporated by reference to page 8 of the Company's Registration Statement
     on Form S-8 (File No. 333-2196).  

(4)  See page 4 hereof.
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 12803}]
{"company-data": {"conformed-name": "CYTYC CORP", "cik": "0000849778", "assigned-sic": "3826", "irs-number": "020407755", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-59291", "film-number": "98667928"}, "business-address": {"street1": "237 CEDAR HILL ST", "city": "MARLBOROUGH", "state": "MA", "zip": "01752", "phone": "5082638000"}, "mail-address": {"street1": "85 SWANSON ROAD", "city": "BOXBOROUGH", "state": "MA", "zip": "01719"}}
As filed with the Securities and Exchange Commission on July 17, 1998

                                                     Registration No. [________]

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

                       SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C.  20549
                              ____________________

                                    FORM S-8

                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933

                               CYTYC CORPORATION
        --------------------------------------------------------------
            (Exact Name of Registrant as Specified in Its Charter)

                   Delaware                                    02-0407755
---------------------------------                      -------------------------
(State or other jurisdiction of                             (I.R.S. Employer
incorporation or organization)                              Identification No.)

                    85 Swanson Road, Boxborough, MA  01719
             -----------------------------------------------------
              (Address of Principal Executive Offices) (Zip Code)
                            _______________________

                                1995 STOCK PLAN
                      ----------------------------------
                           (FULL TITLE OF THE PLAN)
                          __________________________

                              PATRICK J. SULLIVAN
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                               CYTYC CORPORATION
                                85 SWANSON ROAD
                             BOXBOROUGH, MA  01719
                                  (508) 263-8000
                         -----------------------------------------
                      (NAME, ADDRESS AND TELEPHONE NUMBER,
                   INCLUDING AREA CODE, OF AGENT FOR SERVICE)
                              ___________________

                                    COPY TO:

                           JONATHAN M. MOULTON, ESQ.
                        TESTA, HURWITZ & THIBEAULT, LLP
                               HIGH STREET TOWER
                                125 HIGH STREET
                          BOSTON, MASSACHUSETTS 02110
                                 (617) 248-7000
                               
================================================================================

                        CALCULATION OF REGISTRATION FEE

================================================================================
Proposed                Proposed
        Title Of                                          Maximum                Maximum
       Securities                  Amount                Offering               Aggregate            Amount of
          To Be                    To Be                 Price Per               Offering          Registration
       Registered              Registered(1)             Share(2)                 Price                 Fee
-----------------------------------------------------------------------------------------------------------------
1995 STOCK PLAN
Common Stock,
$.01 par value                  454,115 shares                $18.00               $8,174,070           $2,411.35

=================================================================================================================
(1) Pursuant to the terms of the Company's 1995 Stock Plan, an additional
    454,115 shares of Common Stock may be issued effective as of the first
    trading day of 1998 and such additional shares are registered hereby. Upon
    the filing and effectiveness of this Registration Statement on Form S-8, the
    total number of shares of Common Stock registered pursuant to the 1995 Stock
    Plan will be 1,625,615 shares.

(2) None of such shares are subject to outstanding options. The price of $18.00
    per share, which is the average of the high and low prices reported on the
    Nasdaq National Market on July 14, 1998, is set forth solely for
    purposes of calculating the filing fee pursuant to Rule 457(c).

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

   This Registration Statement registers additional securities of the same class
as other securities for which the Registration Statement on Form S-8 (File No.
333-2196), as filed with the Securities and Exchange Commission (the
"Commission") on March 8, 1996 relating to Cytyc Corporation's 1995 Stock Plan, 
and as amended on Form S-8 (File No. 333-22675), as filed with the Commission on
March 3, 1997, is effective. Pursuant to General Instruction E to Form S-8, the
contents of the above-listed Registration Statements are hereby incorporated by
reference.

                                       1
PART II
               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.    Incorporation of Documents by Reference.
           --------------------------------------- 

   The Company previously registered under the Securities Act an aggregate of
1,171,500 shares of Common Stock offered pursuant to the 1995 Stock Plan
pursuant to a Registration Statement on Form S-8 (File No. 333-2196) filed with
the Commission on March 8, 1996, as amended on Form S-8 (File No. 333-22675),
filed with the Commission on March 3, 1997, which are incorporated in this
Registration Statement by reference.

   The following documents filed with the Commission are incorporated by
reference in this Registration Statement:

    (a)  Registrant's Annual Report on Form 10-K for the fiscal year ended
         December 31, 1997 filed pursuant to the Securities Exchange Act of
         1934, as amended (the "Exchange Act");

    (b)  Registrant's Quarterly Report on Form 10-Q for the fiscal quarter ended
         March 31, 1998 filed pursuant to the Exchange Act; and

    (c)  The section entitled "Description of Registrant's Securities to be
         Registered" contained in the Registrant's Registration Statement on
         Form 8-A, filed with the Commission pursuant to Section 12(g) of the
         Exchange Act on January 16, 1996.

    All documents subsequently filed with the Commission by the Registrant
pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act after the
date hereof and prior to the filing of a post-effective amendment which
indicates that all securities offered herein 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 a part hereof from the date
of filing of such documents.

    Any statement contained in any document incorporated, or deemed to be
incorporated, by reference herein shall be deemed to be modified or superseded
for purposes of this Registration Statement to the extent that a statement
contained herein or in any subsequently filed document which also is, or is
deemed to be, incorporated by reference herein modifies or supersedes such
statement.  Except as so modified or superseded, such statement shall not be
deemed to constitute a part of this Registration Statement.

                                       2
Item 8.  Exhibits
         --------

Exhibit No.         Description of Exhibit
-----------         ----------------------

    4(1)            1995 Stock Plan, as amended.

    5(2)            Opinion of Testa, Hurwitz & Thibeault, LLP.
 
    23.1(2)         Consent of Arthur Andersen LLP.

    23.2(2)         Consent of Testa, Hurwitz & Thibeault, LLP (included in
                    Exhibit 5).

    24(3)(4)        Power of Attorney (included as part of the signature page
                    to this Registration Statement).

-----------
(1)  Incorporated by reference to the Company's Registration Statement on 
     Form S-8 (File No. 333-2196), as amended on Form S-8 (File No. 333-22675).

(2)  Filed herewith. 

(3)  Incorporated by reference to page 8 of the Company's Registration Statement
     on Form S-8 (File No. 333-2196).  

(4)  See page 4 hereof.  

                                       3
SIGNATURES

   Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of 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 Boxborough, Commonwealth of Massachusetts, on this
17th day of July, 1998.

                               CYTYC CORPORATION

                               By:     /s/ Patrick J. Sullivan
                                   ---------------------------
                                   Patrick J. Sullivan
                                   President and Chief Executive Officer

                       POWER OF ATTORNEY AND SIGNATURES

   We, the undersigned officers and directors of Cytyc Corporation, hereby 
severally constitute and appoint Patrick J. Sullivan and Joseph W. Kelly, and 
each of them singly, our true and lawful attorneys, with full power to them and 
each of them singly, to sign for us in our names in the capacities indicated 
below, all pre-effective and post-effective amendments to this registration 
statement, and generally to do all things in our names and on our behalf in such
capacities to enable Cytyc Corporation to comply with the provisions of the 
Securities Act of 1933, as amended, and all requirements of the Securities and 
Exchange Commission.  

   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
date indicated.

Signature               Capacity                           Date
---------               --------                           ----

       *                President, Chief Executive     July 17, 1998
-------------------     Officer and Director         
Patrick J. Sullivan     (Principal Executive Officer)
                        

       *                Vice President,                July 17, 1998
-------------------     Chief Financial Officer and    
Joseph W. Kelly         Treasurer                    
                        (Principal Financial and     
                        Accounting Officer)           
                        

/s/ Sally W. Crawford   Director                       July 17, 1998
--------------------- 
Sally W. Crawford

       *                Director                       July 17, 1998
---------------------     
Franklin J. Iris

/s/ William G. Little   Director                       July 17, 1998
--------------------- 
William G. Little

       *                Director                       July 17, 1998
---------------------   
C. William McDaniel

/s/ Anna S. Richo       Director                       July 17, 1998
---------------------                                  
Anna S. Richo

       *                Director                       July 17, 1998
---------------------                           
Monroe Trout, M.D.

*By:  /s/ Patrick J. Sullivan
      -----------------------
      Patrick J. Sullivan
      Attorney-in-Fact

                                       4
EXHIBIT INDEX
                                 -------------
                                        
Exhibit       Description of Exhibit                                    Page No.
-------       ----------------------                                    --------
    4(1)      1995 Stock Plan                                               
 
    5(2)      Opinion of Testa, Hurwitz & Thibeault, LLP                    6
 
    23.1(2)   Consent of Arthur Andersen LLP                                7
 
    23.2(2)   Consent of Testa, Hurwitz & Thibeault, LLP (included in       6
              Exhibit 5)

    24(3)(4)  Power of Attorney (included as part of the signature          4
              page to this Registration Statement).  

-------
(1)  Incorporated by reference to the Company's Registration Statement on 
     Form S-8 (File No. 333-2196) as amended on Form S-8 (File No. 333-22675).

(2)  Filed herewith.  

(3)  Incorporated by reference to page 8 of the Company's Registration Statement
     on Form S-8 (File No. 333-2196).  

(4)  See page 4 hereof.