A multi-site sample of currently-injecting drug users (IDUs) comprising 344 men and 136 women was recruited in Edinburgh. Sixty-seven per cent of the sample said they had at some time used injecting equipment already used by another person and 25% admitted doing so in the 6 months before interview. Whereas women who injected with used equipment obtained it predominantly from a sexual partner, for men the source was more often a close friend or someone whose HIV status they were unlikely to know. In the 6 months before interview, 40% of men, compared with 20% of women, had more than one heterosexual partner. This difference was associated with a higher proportion of men with steady partners also having casual partners. Women IDUs were more likely to have regular partners who injected (57% vs 26%). Though sharing of injecting equipment has already diminished in Edinburgh, further measures are needed to eliminate it. For injectors here, the risk of infection from unprotected heterosexual intercourse may now be greater than that from sharing injecting equipment, particularly for women. Other methods of encouraging changes in sexual behaviour need to be investigated and successful ones promoted.