[Brown, Rudnick, Freed & Gesmer]


                               September 11, 1996


Hologic, Inc.
590 Lincoln Street
Waltham, MA 02154

RE:  Registration Statement on Form S-8
     ----------------------------------

Ladies and Gentlemen:

       We are general counsel to Hologic, Inc., a Delaware corporation (the
"Company"). We have been asked to deliver this opinion in connection with the
preparation and filing with the Securities and Exchange Commission under the
Securities Act of 1933, as amended (the "Act"), of a Registration Statement on
Form S-8 (the "Registration Statement") relating to 297,517 shares of the
Company's Common Stock, $.01 par value (the "Shares") and 297,517 Rights, as
defined below. The Rights are issuable pursuant to that certain Rights
Agreement, dated as of December 22, 1992, as amended by Amendment No. 1 dated
December 14, 1995 (the "Rights Agreement"), providing, in effect, for the
delivery of a right (a "Right"), along with each share of Common Stock issued by
the Company.

       Of the Shares and Rights, (i) 22,370 are issuable upon exercise of
options granted pursuant to the FluoroScan Imaging Systems, Inc. 1994 Amended
and Restated Stock Incentive Plan, (ii) 124,742 are issuable upon exercise of
options granted pursuant to the FluoroScan Imaging Systems, Inc. 1995 Stock
Incentive Plan and (iii) 150,405 are issuable upon exercise of options granted
pursuant to the FluoroScan Imaging Systems, Inc. 1994 Directors Stock Option
Plan. The aforementioned plans (collectively, the "Plans") were assumed by the
Company upon the merger of FluoroScan Imaging Systems, Inc. ("FluoroScan"), with
and into a wholly-owned subsidiary of the Company on August 29, 1996 pursuant to
an Agreement and Plan of Merger dated July 18, 1996 among the Company,
FluoroScan and the Company's subsidiary (the "Merger Agreement").

       In connection with this opinion, we have examined and are familiar with
originals or copies, certified or otherwise identified to our satisfaction, of
the following documents (collectively, the "Documents"):

       1.  A copy of the Certificate of Incorporation of the Company as in
           effect on the date hereof;
 
       2.  A copy of the Bylaws of the Company as in effect on the date hereof;

 
Hologic, Inc
September 11, 1996
Page 2 


       3.  The corporate records of the Company relating to the proceedings of
           stockholders and directors of the Company;
 
       4.  Each of the Plans;

       5.  The Rights Agreement;

       6.  The Merger Agreement; and

       7.  The Registration Statement.

       In giving our opinion, we have relied as to matters of fact upon
certificates of officers of the Company. For purposes of this opinion we have
assumed without any investigation (1) the legal capacity of each natural person
and (2) the genuineness of each signature, the completeness of each document
submitted to us as an original and the conformity with the original of each
document submitted to us as a copy.

       Our opinion hereafter expressed is based solely upon (1) our review of
the Documents, (2) discussions with certain officers of the Company with respect
to the Documents, (3) discussions with those of our attorneys who have devoted
substantive attention to the matters contained herein and (4) such review of
published sources of law as we have deemed necessary.

       Based upon and subject to the foregoing, we are of the opinion that the
Shares have been duly authorized and, when issued in accordance with the terms
of the applicable Plan, the Shares will be validly issued, fully paid and
nonassessable. The Rights have been duly authorized and, when issued in
accordance with the terms of the Rights Agreement, will be validly issued, fully
paid and nonassessable.

       We hereby consent to the filing of this opinion as Exhibit 5.1 to the
Registration Statement and to the reference to our firm wherever it appears in
the Registration Statement.

                              Very truly yours,

                              BROWN, RUDNICK, FREED & GESMER, P.C.
                              By:  Brown, Rudnick, Freed & Gesmer, a partner


                              By: /s/ Philip J. Flink
                                  ---------------------------------------------
                                  Philip J. Flink, a Member
                                  hereunto duly authorized

PJF/LML