To estimate the cost of hospital care for children infected with the human immunodeficiency virus (n = 37) at Harlem Hospital Center, New York, a cost-based inventory of medical resource consumption was developed. Six thousand thirty-five inpatient days were audited by retrospective chart review. The total cost of care between 1981 and 1986 was +3,362,597. Average lifetime costs were +90,347 per child. One third of the total inpatient days and over 20% of the cost resulted from social rather than medical factors. Per diem costs were highest for children with opportunistic infections (+705) and lowest for homeless "boarder babies" (+466). Boarder babies had a mean length of stay nearly four times longer than those with homes (339 days vs 89 days). The primary predictors of length of stay were maternal intravenous drug use and boarder baby status, regardless of medical need. The unique needs of human immunodeficiency virus-infected children require innovative medical, social, and financial solutions.