This study documents the prevalence and correlates of post-traumatic stress disorder (PTSD) among Australian individuals with heroin dependence. Data was obtained from a cohort of 615 people dependent on heroin, 535 entering treatment for their heroin dependence and 80 individuals not in treatment. Trauma exposure (92%) and lifetime PTSD (41%) were highly prevalent. PTSD was prevalent across all treatment modalities, most commonly residential rehabilitation (52%) followed by maintenance therapies (42%), and detoxification (37%). The lowest prevalence was reported among those not in treatment (30%). Although men and women were equally likely to have experienced trauma (93% vs. 89%), women were more likely to develop lifetime PTSD (61% vs. 37%). For the large majority of those with PTSD, the condition was chronic (84%), with symptoms continuing for an average of 9.5 years. Those with PTSD had more extensive polydrug use histories, poorer general physical and mental health, and more extensive health service utilisation. It is concluded that PTSD is highly prevalent among individuals with heroin dependence, presenting a significant challenge to treatment providers.