The cost of HIV/AIDS care was measured in Belgium in 1996. This paper is concerned with direct costs (formal and informal care). This is a prospective study, stratified by CDC-disease stage. A societal point of view was chosen. Eighty-two sequential patients agreed to join the study during outpatient visits. Data on service use and costs were obtained through a care-cost diary kept over three months. Half of the patients (41) returned a completed diary, which reduced the sample size considerably. Additional billing data were obtained from different sources and by calculating the time spent for certain services. In stage A (asymptomatic HIV), the mean (+/- SD) annual total direct costs are US$2,373 (2,079), rising to US$8,401 (7,520) in stage B (symptomatic HIV) and ending up at US$27,373 (22,087) in stage C (full blown AIDS). A difference in balance of costs at different stages of disease was observed. The principal cost of outpatient pharmaca in HIV patients is overtaken by the cost of hospitalization in AIDS patients. The cost of informal care is considerable (40% of the total cost) from stage B onwards. Health care use and costs increase with severity of illness.