During a one year period from August 1992 to August 1993, 272 injecting drug users attending the National Drug Treatment Centre were tested for antibody to Hepatitis C Virus with a second generation EIA test. The overall sero-prevalence was 84% (N = 229). A significantly greater proportion of females tested positive than males (Female: Male, 94% v 80%, p < 0.012). Looking at sero-prevalence of Hepatitis C in relation to duration of intravenous drug misuse, we found that in those patients with a duration of misuse of greater than two years (N = 156) the sero-prevalence was 95% and in those with a duration of intravenous drug misuse of less than two years (N = 116) the sero-prevalence was 70%. We conclude that needle sharing continues to occur among injecting drug users during their first two years of injecting, despite the existence of harm minimization programmes. Our results would suggest that female injecting drug users are involved in greater at risk behaviour in relation to Hepatitis C than their male counterparts.