Disabled workers who start receiving Social Security Disability Income (SSDI) must wait twenty-four months to qualify for Medicare. Legislation introduced in Congress would eliminate this waiting period, to guarantee that people with disabilities severe enough to qualify for SSDI will not be uninsured. We provide a longitudinal view of Medicare enrollment before age sixty-five by following a national sample of people ages 55-64. One person in six was covered by Medicare before turning sixty-five. A quarter of new enrollees were uninsured during the waiting period. There were great disparities in reliance on Medicare and coverage in the waiting period.