AIM: To investigate the frequency of non-fatal cocaine overdose, and responses to overdoses, among injecting and non-injecting cocaine users. DESIGN: Cross-sectional study. SETTING: Sydney, Australia. PARTICIPANTS: Two hundred current cocaine users. MEASUREMENTS: Structured interview. FINDINGS: Thirteen per cent of the sample had overdosed on cocaine, 7% in the preceding 12 months. Cocaine injectors were more likely to have overdosed, both ever (17 v 6%) and in the preceding 12 months (9 v 3%). The most common symptoms of overdose were palpitations (68%), intense sweating (44%) and seizures (40%). The use of other drugs in combination with cocaine prior to the most recent overdose was prevalent (64%), most commonly opioids (40%), alcohol (24%) and cannabis (24%). Those who had overdosed were more likely to be female, had longer cocaine use careers, had used more cocaine in the preceding month and preceding 6 months, had higher levels of cocaine dependence and more extensive polydrug use. Twenty-four per cent had witnessed a cocaine overdose, 13% in the preceding 12 months. Injectors were more likely to have witnessed overdoses, both ever (35% v 8%) and in the preceding 12 months (20% v 3%). CONCLUSIONS: Experience of, and exposure to, overdose were not rare events. Cocaine users need to be aware of the possibility and nature of overdose, and that cocaine overdose can occur irrespective of method of use. There is a need to emphasise the potential danger of combining cocaine with other drugs.