Social Security and Medicare Lock-Box Act

Amends title II (Old Age, Survivors and Disability Insurance) (OASDI) of the Social Security Act to establish in the Federal Old-Age and Survivors Insurance Trust Fund a Social Security Surplus Protection Account to hold the Social Security surplus for the fiscal year of the sum of Social Security taxes collected, as well as the aggregate increase in certain tax liabilities, over the sum of benefits paid.

Establishes in the Federal Hospital Insurance Trust Fund a Medicare Surplus Protection Account to hold amounts equivalent to the Medicare part A surplus for the fiscal year of the sum of hospital insurance taxes collected over the sum of Medicare part A benefits paid.

Denies the availability of the balance in either Account for investment by the Managing Trustee.

Establishes in the executive branch a Social Security and Medicare Part A Investment Commission to study the most effective vehicles for investment of the Federal Old-Age and Survivors Insurance Trust Fund and the Federal Hospital Insurance Trust Fund (other than investment in the form of U.S. obligations).