This profile of Medicare beneficiaries with acquired immunodeficiency syndrome (AIDS) was developed by applying a casefinding algorithm to virtually all Medicare claims from 1991-93. The algorithm identified more than 37,000 beneficiaries with AIDS, approximately 21,000 of whom were living at the end of 1993. These estimates suggest that as many as 12 percent of people living with AIDS at the end of 1993 were covered by Medicare. Medicare expenditures for these beneficiaries averaged more than $2,400 per month and totaled more than $500 million in 1993. These expenditures are likely to rise as more people with AIDS live long enough to qualify for Medicare coverage.