Program enacted in 1965 under Title XVIII of the Social Security Amendments of 1965 to provide medical benefits to those 65 and over. The program has two parts: Part A, Hospital Insurance, and Part B, Supplementary Medical Insurance. Retired workers qualified to receive Social Security benefits, and their dependents, also qualify for the hospital insurance portion. The program is paid for by payroll taxes on employees and covered workers. The supplementary medical insurance provides additional coverage on a voluntary basis for physician services. Those enrolled in the program pay a monthly premium. Coverage is also available to persons under 65 who are disabled and have received Social Security disability benefits for 24 consecutive months.