Medicare is a health insurance program for people 65 years of age and older, some disabled people under 65 years of age, and people with end-Stage Renal Disease (permanent kidney failure treated with dialysis or a transplant). Medicare has two parts. Part A is hospital insurance. Most people do not have to pay for Part A. Part B is medical insurance. Most people pay monthly for Part B. Everyone eligible for Social Security Disability Insurance (SSDI) benefits is also eligible for Medicare after a 24-month qualifying period.