This study evaluated the effectiveness of a brief intervention (BI), a one-session motivational interview, in reducing HIV risk-taking behaviour among injecting drug users (IDU) not enrolled in any form of treatment for drug dependence. IDU were randomly assigned to either BI or a non-intervention control condition (NIC). One hundred and twenty-one subjects were successfully contacted for a 3-month follow-up and 88 subjects were followed up at 6 months. There were significant reductions for the sample as a whole for injecting risk-taking subscale scores on the HIV Risk-taking Behaviour Scale between pre-treatment and follow-up. There was no significant change in sexual risk-taking behaviour. There were no significant differences between groups on any measure at 3- and 6-month follow-up. There are a number of possible reasons why the sample as a whole showed significant improvements from initial to follow-up assessments. It is possible that, having had their attention directed to their risk-taking behaviour, subjects attempted to reduce their injecting risk-taking behaviour. If this is the case and subjects in the NIC condition can be considered as having received a BI, this suggests that BIs involving a personal risk assessment are effective in reducing risk behaviours associated with injecting. However, this suggestion could only be confirmed by comparison with a non-assessment control group.