Medicare is a health insurance program for people 65 years old or over and for certain disabled people under 65. A person is automatically enrolled in Medicare hospital insurance (Part A) when he or she applies for Social Security benefits upon reaching 65. Part A covers inpatient care in a hospital or skilled nursing facility for a limited period of time. Part B covers doctor's services and outpatient hospital services. This is paid for out of the enrollee's Social Security. Medicare does not pay full cost of some covered services.