Until 1999 the known prevalence of HIV in Indonesia was low, except for isolated geographic groups exposed to Thai fisherman. Since then, the prevalence among injection drug users in rehabilitation centers in Jakarta has risen rapidly to approximately 45-48%, according to surveys in 2001. By 2002 the prevalence had risen to 8-17% among female sex workers, 22% among transvestite sex workers, and 4% among other male sex workers. Condom use is low in all groups, and there is considerable sexual mixing between risk groups. Surveys suggest that an increasing proportion of adolescents use drugs and have had sexual intercourse. Thus, although the epidemic in Indonesia is currently in the World Health Organization-defined "concentrated stage," all the ingredients for rapid spread are present. Intensive effective intervention strategies-condom use and clean needle use promotions-need to be implemented, especially in the high-risk groups, if a more serious epidemic is to be averted.