Hospitals are significant resources for care of HIV/AIDS patients. Previous studies that have attempted to identify and track the characteristics of these patients and their hospitalizations have been limited in their ability to produce national estimates of patient use of such resources. This study, using data from the Healthcare Cost and Utilization Project (HCUP-3) attempted to characterize and estimate the cost of hospital usage by HIV/AIDS patients. We estimate that in 1994 approximately 188,506 admissions of HIV/AIDS patients occurred with an average charge of $19,244 U.S. per admission, for an estimated total cost of $3.63 billion. Compared with non-HIV-infected patients, HIV/AIDS patients tended to be male (75.83% versus 41.49%), a member of a minority group (53.51% versus 20.77%), hospitalized in a private, nonprofit, urban teaching hospital with a longer average length of stay (10.27 versus 5.52 days), and to have a higher in-hospital mortality (11.45% versus 2.58%). Approximately half of the hospital charges (47%) for these admissions were absorbed by Medicaid, and 25% by private insurance. The remainder of the charges were borne by the patients themselves. The results presented here for 1994 predate the widespread use of protease inhibitor/ highly active antiretroviral therapy (HAART), thus making this study an important benchmark for the delineation of the effects of HAART and any other future developments in HIV therapy on the characteristics of HIV/AIDS patient resource use on a national level. This study further demonstrates that HCUP is a powerful tool for the estimation and costing of hospital resource use.