Prisons pose unique public and mental health problems. Many prisoners are poorly educated, of limited intelligence, behaviorally impaired, and often drug addicted. They are crowded together in communal facilities with marginal provisions for sanitation. In some systems, nearly 20% of newly incarcerated prisoners are HIV infected, posing a direct risk to other prisoners through sexual assault. Indirectly, HIV infection poses a risk through its suppression of normal immune system function, increasing the chance of infection with diseases such as tuberculosis that are easily spread to others. More critically, providing humane care for HIV-infected prisoners is outstripping the prison health resources in the states with substantial HIV-infected prisoner populations.