Vancouver has experienced an explosive HIV epidemic despite the presence of a needle exchange programme (NEP). We sought possible explanations for high-risk syringe sharing among Vancouver injection drug users over the period January 1999 to October 2000. Overall, 14% of participants reported high-risk sharing. Although acquiring needles exclusively from the NEP was independently associated with less sharing, we identified several risk factors for persistent sharing, including difficulty accessing sterile needles, bingeing, and frequent cocaine injection.