To examine a possible link between substance use and risky sexual behaviour, a cross-sectional study was conducted among 357 inmates across four south african prisons involved in a pre-release intervention programme for parolees. About 93% of the participants reported using alcohol and 52% used marijuana prior to imprisonment, while 56% reported previous occurrence of sexually transmitted infections (stis). Logistic regression analyses explored the impact of substance use on intention to reduce risky sexual behaviour. Age and inconsistent use of condoms were positively associated with having an sti prior to incarceration, while reported alcohol and marijuana intake had no effect. Never using condoms before was highly associated with lower intention to engage in preventive behaviours upon release. It can be concluded that inmates demonstrate high levels of substance use and engagement in risky sexual behaviours. Targeted pre-release substance abuse interventions are essential to reduce the burden of disease amongst offenders.