Social Security Investment Reform Act of 1991

Social Security Investment Reform Act of 1991 - Amends titles II (Old Age, Survivors and Disability Insurance) and XVIII (Medicare) of the Social Security Act to direct the Managing Trustees of the Federal Old-Age and Survivors Insurance Trust Fund, Federal Disability Insurance Trust Fund, and Federal Hospital Insurance Trust Fund (trust funds) to immediately invest that portion of the trust funds which is not required for current withdrawals. Prohibits the sale and redemption of trust fund assets or the expenditure of trust fund amounts for purposes other than those specified in such titles. Requires members of such trust funds' Boards of Trustees to faithfully execute their duties, but does not impose a fiduciary duty.

Requires that, in consideration of the public debt limit, required investment of funds or amounts over which the Secretary of the Treasury has investment authority occur prior to the issuance of other obligations.

Requires the Boards of Trustees of the trust funds to meet at least twice each year. Sets forth provisions requiring reports by the Boards of Trustees and the Managing Trustees to the Congress regarding the operation and status of the trust funds.