In developing countries, access to antiretroviral therapy (ART) is improving as HIV treatment becomes a greater priority in the global fight against AIDS. While ART has clearly beneficial clinical effects, increased access to treatment may also affect sexual behaviour. To examine the strength of evidence for the impact of medical treatment for HIV-positive individuals on behavioural outcomes in developing countries, we conducted a comprehensive search of the peer-reviewed literature. Studies were included if they provided clinical treatment to HIV-positive individuals in a developing country, compared behavioural, psychological, social, care, or biological outcomes related to HIV-prevention using a pre/post or multi-arm study design, and were published between January 1990 and January 2006. Only three studies were identified that met the inclusion criteria. All were conducted in Africa, utilized before/after or multi-arm study designs, and relied on self-reported behaviour. In all three studies, a majority of HIV-infected individuals reported being sexually abstinent, and access to ART was not associated with an increase in HIV-related risky sexual behaviours. However, one cross-sectional study found that ART patients were more likely to report STD treatment. The available evidence indicates a significant reduction in risk behaviour associated with ART in developing countries. However, there are few existing studies and the rigor of these studies is weak. More studies are needed to build an evidence base on which to make programmatic and policy decisions.