A sample of 312 heroin users were interviewed about their experience of non-fatal heroin overdose. Non-fatal overdose was common, with 61 % of subjects reporting one, on a median of 2 occasions. Those subjects who had used heroin in the preceding 6 months were interviewed about overdose risk perceptions and risk behaviours (n = 266). The majority of these subjects (80%) believed they had a low risk of overdose, there being no difference in risk perception between those who had overdosed in the last 6 months and those who had not. While the majority (73%) claimed to use various strategies to avoid overdose, these were sporadically practised. Those who had overdosed in the past 6 months had used heroin on more days in that time, had higher levels of heroin dependence, more often used alcohol and benzodiazepines in combination with heroin, and were less likely to be enrolled in methadone maintenance during that time. Methadone maintenance thus had a protective effect against overdose, even for patients who continued heroin use over the preceding 6 months.