Medicare Universal Coverage Expansion Act of 1991 - Amends titles II (Old Age, Survivors and Disability Insurance) (OASDI) and XVIII (Medicare) of the Social Security Act to provide Medicare coverage for all American citizens regardless of their age.

Amends the Medicare program to: (1) make the program the primary payor for health care items and services; (2) expand coverage of preventive health care services to include preventive services related to pregnancy and, if otherwise allowed as a preventive service, routine physical checkups; and (3) establish a new financing mechanism for Medicare part B (Supplementary Medical Insurance) based entirely on Government contributions.

Amends the Internal Revenue Code to: (1) remove the limitation on the amount of wages that are subject to the hospital insurance tax; and (2) increase the applicable rates of the hospital insurance tax in order to provide sufficient funding for the new Medicare program.

Provides for the transfer from the OASDI Trust Fund to the Federal Hospital Insurance Trust Fund (Medicare part A trust fund) of any surplus amounts.

Amends the Medicare program to provide for the transfer from the Medicare part A trust fund to the Federal Supplementary Medical Insurance Fund of any amounts needed for the new Medicare program.