Previous investigation has suggested that the direct cost of medical care for the 24 011 reported patients with acquired immunodeficiency syndrome (AIDS) may be as high as $147 000 per patient. To evaluate the use and cost of medical services for patients with AIDS in Massachusetts, we performed a one-year cost of illness study of 45 AIDS patients. Sociodemographic and clinical data as well as information on medical utilization were obtained from review of outpatient and hospital records. Patients with AIDS required a mean of 3.3 (±3.2) hospitalizations per year and 18.4 (±21.8) ambulatory visits per year. Overall, medical costs averaged $46 505 ±$38 720 per patient per year, with 91 % of these expenditures related to use of inpatient services. These results suggest that the cost of medical care for AIDS patients may be substantially less than previously estimated. (JAMA 1986;256:3107-3109)