Adherence, the act of following a course of medication in exactly the manner prescribed, is critical for the success of therapy. Adherence is influenced by many behavioural and social factors and incarceration might be one such factor. This study determined the level of adherence and reasons for non-adherence to antiretroviral therapy among 93 HIV-infected prisoners. Up to 56% of these patients had poor adherence. A similar rate of adherence was detected in prisoners after release. Problems with antiretroviral adherence among prisoners appear to be mostly linked to their deviant behaviour. Inmates with poor adherence had higher HIV-related morbidity and mortality. Age and country of origin were also associated with adherence.