BACKGROUND Hepatitis B infection in injecting drug users is an important public health problem. Active immunization against hepatitis B is immunogenic and safe, but uptake rates in targeted vaccination programmes are low. This study was undertaken to identify factors associated with the uptake of hepatitis B vaccination in injecting drug users attending a needle exchange service. METHODS A retrospective cross-sectional survey of case-note data of injecting drug users who had no markers of hepatitis B infection or immunity was undertaken within a drop-in needle exchange service for injecting drug users in a large urban area in England. A qualitative study using semi-structured interviews with needle exchange staff was also conducted. RESULTS Of 207 injecting drug users, 180 (87 per cent) had been offered vaccine, 123 (59 per cent) accepted at least one dose and 55 (27 per cent) received three or more doses. Vaccine was less likely to be offered to those sharing injecting equipment or known to have hepatitis C. Needle sharing was also associated with failure to accept vaccine, as was increasing age and the length of contact with the service. CONCLUSIONS Those who are most at risk are least likely to be offered vaccine and accept it. This calls into doubt the effectiveness of hepatitis B vaccination strategies targeted at high-risk groups and adds weight to arguments for universal vaccination.