We reviewed published studies reporting the direct medical costs of treating HIV-infected people in countries using highly active antiretroviral therapy (HAART). Of 543 potentially relevant studies, only nine provided adequate data to make a meaningful statement about costs. Within studies, people with more advanced disease incurred higher total costs. Valid comparisons of total direct medical costs between studies were not possible because of differences in the specific components included, the heterogeneous nature of study populations in terms of disease stage, the sources and methods used to estimate unit costs, and the level of aggregation at which results were reported. The advent of HAART has major implications for the cost of treating HIV-infected individuals. Although this information is important for planning purposes, only a small number of published studies provide useful estimates of the direct cost. A useful method of estimating resource use and costs is computer simulation.