Although the potential for prisons to act as the setting for HIV transmission has been recognised, there is an enduring lack of knowledge in this area. Data are presented on patterns of injecting and sharing in Edinburgh prison (Scotland), 1993-1994. There was a relatively low level of injecting in Edinburgh prison during this period, with 13% (8/60) of a sample of drug users having injected at some point during their current sentence. The majority (6/8) of those who had injected had shared injecting equipment. Where sharing took place, the level of HIV risk was variable, but would have been higher had cleaning fluids not been available within the prison, or had they not been used by sharers. The implications of this study for drug service provision in prisons is discussed.