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):

                               September 29, 1998

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


                         THERMO INSTRUMENT SYSTEMS INC.
             (Exact name of Registrant as specified in its charter)


Delaware                       1-9786                          04-2925809
(State or other              (Commission                    (I.R.S. Employer
jurisdiction of               File Number)               Identification Number)
incorporation or
organization)


860 West Airport Freeway
Suite 301
Hurst, Texas                                                     76054
(Address of principal executive offices)                      (Zip Code)


                                 (817) 485-6663
                         (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 Thermo
Instrument  Systems Inc.'s Annual Report on Form 10-K for the year ended January
3, 1998. These include risks and uncertainties  relating to: Thermo Instrument's
acquisition  and  spinout  strategies,  competition  and  technological  change,
intellectual   property  rights  and  litigation,   dependence  on  certain  key
industries  and  international  operations,  possible  changes  in  governmental
regulations, capital spending and government funding policies, and the potential
impact of the year 2000 on processing date-sensitive information.

Item 5.     Other Events

     On September 29, 1998, Thermo Instrument Systems Inc. ("Thermo Instrument")
issued a press release announcing that it will record  approximately $28 million
in pretax  restructuring and other charges in the third quarter,  ending October
3, 1998.  Thermo  Instrument will incur  approximately  $17 million in severance
expenses  resulting  from a reduction in its  workforce of  approximately  seven
percent  (between 650 and 700 employees).  In addition,  Thermo  Instrument will
record  approximately $11 million of inventory  write-downs and facility closing
costs.  These charges will reduce third quarter 1998 diluted  earnings per share
by  approximately  $.10.  Thermo  Instrument  estimates  that these actions will
result in 1999 operating savings of approximately $28 million.

      Each Thermo  Instrument  subsidiary has examined its own circumstances and
has defined the actions necessary to reduce costs and improve operating income.

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 29th day of September, 1998.



                                    THERMO INSTRUMENT SYSTEMS INC.


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