OBJECTIVE: To investigate the prevalence and associations of buprenorphine injection among a field-recruited cohort of injecting drug users. DESIGN: Cross-sectional data from a prospective longitudinal cohort. Setting. Metropolitan Melbourne, Australia. SUBJECTS: Current injecting drug users (IDUs). MAIN OUTCOME MEASURES: Prevalence of buprenorphine injection, associations with location, buprenorphine as prescribed pharmacotherapy, markers of hepatitis C virus (HCV) exposure and risk behaviours for HCV. RESULTS: More than 10% of our 316 participants reported buprenorphine as the drug they had most often injected, and 32% had injected buprenorphine at least once in the 3 months prior to interview. Primary buprenorphine injection was significantly more likely to be reported by IDUs recruited at one of our three research sites, and by those being prescribed buprenorphine for opioid dependence. Frequency of sharing a used needle was also associated with buprenorphine injection, but HCV exposure was not. CONCLUSIONS: Buprenorphine injection has become entrenched among some groups of Victorian IDUs. The practice carries serious risks to health, including some related to microbiological contamination of buprenorphine during diversion. While measures can be taken to reduce the occurrence of buprenorphine diversion and injection and the associated harm, an alternative harm reduction measure would be to provide IDUs with an injectable pharmacotherapy.