The effects of sociodemographic factors on health service use among people with human immunodeficiency virus (HIV) infection are assessed. Data are from a survey of 939 clients of the Robert Wood Johnson Foundation's AIDS Health Services Program in nine communities across the country. Dependent variables are the number of outpatient visits, use of the emergency room, and whether the respondent had been admitted as an inpatient. In the 3 months before the interview, the sample averaged 7.46 outpatient physician/clinic visits: 35.9% reported an emergency room visit, and 29.9% had been hospitalized. The data suggested differential patterns of health service use, such that those who are white, male, and non-intravenous drug users have higher rates of outpatient clinic/physician use, whereas those who are nonwhite, female, and intravenous drug users have higher rates of emergency room use. Whether these observed differences are attributable to the system's response to different socioeconomic groups, or to differences in individual orientations toward use of medical care is discussed.