This paper examines housing as a contextual factor affecting drug and sexual risk behaviors among HIV positive people using pooled interview data from 2149 clients presenting for services at 16 medical and social service agencies participating in a multi-site evaluation study. The odds of recent drug use, needle use or sex exchange at the baseline interview was 2-4 times as high among the homeless and unstably housed compared to persons with stable housing. Follow-up data collected 6-9 months after baseline showed that change in housing status was associated with change in risk behaviors. Persons whose housing status improved between baseline and follow-up significantly reduced their risks of drug use, needle use, needle sharing and unprotected sex by half in comparison to individuals whose housing status did not change. In addition, for clients whose housing status worsened between baseline and follow-up, their odds of recently exchanging sex was over five times higher than for clients whose housing status did not change. The provision of housing is a promising structural intervention to reduce the spread of HIV.