<PAGE>

                      SECURITIES AND EXCHANGE COMMISSION

                            Washington, D.C. 20549

                                  FORM 10-Q/A


        [X]  Quarterly report pursuant to section 13 or 15 (d)
                  of the Securities Exchange Act of 1934.

             For the Quarterly period ended September 30, 1999

        [_]  Transition report pursuant to section 13 or 15 (d) of the
               Securities Exchange Act of 1934.

        For the transition period from ________________ to ______________.

                        Commission file number 0-17676
                                               -------


                        AMERINST INSURANCE GROUP, INC.
                        ------------------------------
            (Exact Name of Registrant as Specified in its Charter)


DELAWARE                                                     52-1534560
(State or other jurisdiction of                              (I.R.S. Employer
Incorporation or Organization)                               Identification No.)

2386 Airport Road, Barre, Vermont                            05641
Mailing address:  P.O. Box 1330, Montpelier, Vermont         05601
(Address of Principal Executive Offices)                     (Zip Code)

Registrant's telephone number, including area code:          (802) 229-5042

Indicate by check mark whether the Registrant (1) has filed all reports required
to be filed by Section 13 or 15 (d) of the Securities Exchange Act of 1934
during the preceding 12 months (or for such shorter period that the Registrant
was required to file such reports) and (2) has been subject to such filing
requirements for the past 90 days.

                             [X] YES        [_] NO

Number of shares of common stock outstanding:

                                         Number outstanding
     Class                               as of November 5, 1999
     -----                               -----------------------

$0.01 par value common                           331,939
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                                    Part II


The Registrant hereby amends Item 4 of Part II of its Quarterly Report on Form
10-Q filed on November 15, 1999 as follows:


Item 4    Submission of Matters to a Vote of Security Holders.

On August 11, 1999, AIIG held a special meeting of shareholders. At the meeting,
the following matters were approved by a majority of the shareholders:

1)   the proposal to approve and adopt the Exchange Agreement dated as of
     January 20, 1999 between AmerInst Insurance Group, Inc. and AmerInst Group,
     Ltd; and

2)   the proposal to dissolve and liquidate AmerInst Insurance Group, Inc.

The following table provides the number of votes cast for or against, as well as
the number of abstentions, as to each matter submitted to a vote of stockholders
at the meeting.

Matter                                  For            Against        Abstain
------                                  ---            -------        -------

Approval and adoption of                182,064        20,331         3,524
the Exchange Agreement

Dissolution and Liquidation of          183,344        19,259         3,316
AmerInst Insurance Group, Inc.

                                       2

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The Registrant hereby amends Item 6 of Part II of its Quarterly Report on Form
10-Q filed on November 15, 1999 as follows:

Item 6.  Exhibits and Reports on Form 8-K
-----------------------------------------

     (a) Exhibits

         See Index to Exhibits.

     (b) Reports on Form 8-K

         No reports on Form 8-K were filed during the quarter ended
         September 30, 1999.

                                       3
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AMERINST INSURANCE GROUP, INC.

INDEX TO EXHIBITS

Exhibit
Number    Description
-------   -----------

3(i)      Certificate of Incorporation of the Company (1)

3(ii)     Bylaws of the Company (1)

4.1       Article Fourth of Certificate of Incorporation -- included in Exhibit
          3(i) above

4.2       Statement of Stock Ownership Policy, as amended (7)

10.1      Reinsurance Treaty between AIIC and Virginia Surety Company, Inc. (2)

10.2      Agreement between Country Club Bank and AIIC (2)

10.3      Agreement between Country Club Bank and AIIG (2)

10.4      Reinsurance Treaty between AIIC and CNA Insurance Companies (3), 1994
          placement slip (4) 1995 placement slip (5) 1996 placement slip (6)
          1997 placement slip (9) 1998 placement slip (10) and Reinsurance
          Treaty between AIIC and CNA Insurance Companies effective July 1, 1999
          (filed herewith)

10.5      Management Agreement between Vermont Insurance Management, Inc. and
          AIIC dated May 1, 1997 (8) Addenda to Management Agreement dated July
          1, 1997 (9) Addenda to Management Agreement dated July 1, 1998 (10)

10.6      Escrow Agreement among AIIC, United States Fire Insurance Company and
          Harris Trust and Savings Bank dated March 7, 1995 (5)

10.7      Security Trust Agreement among AIIC, Harris Trust and Savings Bank and
          Virginia Surety Company, Inc. dated March 9, 1995 (5)

10.8      Investment Advisory Agreement For Discretionary Accounts between
          Amerinst Insurance Company and Harris Associates L.P. dated as of
          January 22, 1996, as amended by the Amendment to Investment Advisory
          Agreement for Discretionary Accounts dated as of April 2, 1996 (10)

10.9      Exchange Agreement between the Company and AIG Ltd., dated as of
          January 20, 1999 (11)

27        Financial Data Schedule (filed herewith)

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

(1) Filed with the Company's Registration Statement on Form S-1, Registration
    No. 33-17421 and incorporated herein by reference.

(2) Filed with the Company's Annual Report on Form 10-K for the year ended
    December 31, 1992 and incorporated herein by reference.

(3) Filed with the Company's Annual Report on Form 10-K for the year ended
    December 31, 1993 and incorporated herein by reference.

(4) Filed with the Company's Annual Report on Form 10-K for the year ended
    December 31, 1994 and incorporated herein by reference.

(5) Filed with the Company's Quarterly Report on Form 10-Q for the quarter ended
    September 30, 1995 and incorporated herein by reference.

(6) Filed with the Company's Quarterly Report on Form 10-Q for the quarter ended
    September 30, 1996 and incorporated herein by reference.

                                       4
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AMERINST INSURANCE GROUP, INC.

INDEX TO EXHIBITS--Continued


(7) Filed with the Company's Annual Report on Form 10-K for the year ended
    December 31, 1996 and incorporated herein by reference.

(8) Filed with the Company's Quarterly Report on Form 10-Q for the quarter ended
    June 30, 1997 and incorporated herein by reference.

(9) Filed with the Company's Quarterly Report on Form 10-Q for the quarter ended
    September 30, 1997 and incorporated herein by reference.

(10) Filed with the Company's Quarterly Report on Form 10-Q for the quarter
     ended September 30, 1998 and incorporated herein by reference.

(11) Filed with the Company's Annual Report on Form 10-K for the year ended
     December 31, 1998 and incorporated herein by reference.

                                       5
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                                  SIGNATURES
                                  ----------


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.



                                         AMERINST INSURANCE GROUP, INC.
                                         ------------------------------
                                                    (Registrant)



November 19, 1999   Bruce W. Breitweiser
                    ----------------------------------
                    Bruce W. Breitweiser
                    (President and Chief Financial Officer,
                    duly authorized to sign this Report in such
                    capacity and on behalf of the Registrant.)

                                       6