SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

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


                                    FORM 8-K


                                 CURRENT REPORT

                       Pursuant to Section 13 or 15(d) of
                       the Securities Exchange Act of 1934



                                 Date of Report
                      (Date of earliest event reported):

                                December 14, 1998

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


                             THERMOTREX CORPORATION
             (Exact name of Registrant as specified in its charter)


Delaware                        1-10791                   52-1711436
(State or other               (Commission              (I.R.S. Employer
jurisdiction of               File Number)             Identification Number)
incorporation or
organization)


10455 Pacific Center Court
San Diego, California                                         92121 
(Address of principal executive offices)                    (Zip Code)


                                 (619) 646-5300
                         (Registrant's telephone number
                              including area code)



<PAGE>








      This Form 8-K contains forward-looking statements that involve a number of
risks and  uncertainties.  Important  factors that could cause actual results to
differ  materially from those indicated by such  forward-looking  statements are
set forth under the heading  "Forward-looking  Statements"  in Exhibit 13 to the
Registrant's  Annual Report on Form 10-K for the fiscal year ended September 27,
1997. These include risks and uncertainties relating to: product development and
commercialization,  market  acceptance,  government  regulation  and  healthcare
reform,  patient  reimbursement,  competition,  management of growth, ability to
attract  qualified  personnel,  intellectual  property  rights  and  litigation,
product liability, dependence on significant OEM relationships, the Registrant's
acquisition and spinout strategies, and the potential impact of the year 2000 on
processing date-sensitive information.

Item 5.     Other Events

      On December  14,  1998,  Trex  Medical  Corporation  ("Trex  Medical"),  a
majority-owned,  publicly traded  subsidiary of the  Registrant,  issued a press
release  regarding (i) the  resignation  of Trex  Medical's  president and chief
executive officer, Hal Kirshner,  and (ii) Trex Medical's  anticipation that its
earnings  for  its  first  fiscal  quarter,  ending  January  2,  1999,  will be
approximately breakeven due to lower-than-expected revenues.


Item 7.     Financial Statements, Pro Forma Financial Information and Exhibits

      (a)    Financial Statements of Business Acquired: not
            applicable.

      (b)   Pro Forma Financial Information: not applicable.

      (c)   Exhibits: not applicable.






<PAGE>




                                    SIGNATURE



      Pursuant to the  requirements of the Securities  Exchange Act of 1934, the
Registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned, thereunto duly authorized, on this 14th day of December, 1998.



                                          THERMOTREX CORPORATION


                                          By:/s/ Kenneth J. Apicerno
                                             Kenneth J. Apicerno
                                             Treasurer
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SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

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

                                    FORM 8-K

                                 CURRENT REPORT

                       Pursuant to Section 13 or 15(d) of
                       the Securities Exchange Act of 1934

                                 Date of Report
                      (Date of earliest event reported):

                                December 14, 1998

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

                             THERMOTREX CORPORATION
             (Exact name of Registrant as specified in its charter)

Delaware                        1-10791                   52-1711436
(State or other               (Commission              (I.R.S. Employer
jurisdiction of               File Number)             Identification Number)
incorporation or
organization)

10455 Pacific Center Court
San Diego, California                                         92121 
(Address of principal executive offices)                    (Zip Code)

                                 (619) 646-5300
                         (Registrant's telephone number
                              including area code)
This Form 8-K contains forward-looking statements that involve a number of
risks and  uncertainties.  Important  factors that could cause actual results to
differ  materially from those indicated by such  forward-looking  statements are
set forth under the heading  "Forward-looking  Statements"  in Exhibit 13 to the
Registrant's  Annual Report on Form 10-K for the fiscal year ended September 27,
1997. These include risks and uncertainties relating to: product development and
commercialization,  market  acceptance,  government  regulation  and  healthcare
reform,  patient  reimbursement,  competition,  management of growth, ability to
attract  qualified  personnel,  intellectual  property  rights  and  litigation,
product liability, dependence on significant OEM relationships, the Registrant's
acquisition and spinout strategies, and the potential impact of the year 2000 on
processing date-sensitive information.

Item 5.     Other Events

      On December  14,  1998,  Trex  Medical  Corporation  ("Trex  Medical"),  a
majority-owned,  publicly traded  subsidiary of the  Registrant,  issued a press
release  regarding (i) the  resignation  of Trex  Medical's  president and chief
executive officer, Hal Kirshner,  and (ii) Trex Medical's  anticipation that its
earnings  for  its  first  fiscal  quarter,  ending  January  2,  1999,  will be
approximately breakeven due to lower-than-expected revenues.

Item 7.     Financial Statements, Pro Forma Financial Information and Exhibits

      (a)    Financial Statements of Business Acquired: not
            applicable.

      (b)   Pro Forma Financial Information: not applicable.

      (c)   Exhibits: not applicable.
SIGNATURE

      Pursuant to the  requirements of the Securities  Exchange Act of 1934, the
Registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned, thereunto duly authorized, on this 14th day of December, 1998.

                                          THERMOTREX CORPORATION

                                          By:/s/ Kenneth J. Apicerno
                                             Kenneth J. Apicerno
                                             Treasurer