Aims. In Dublin, harm reduction strategies have greatly expanded since 1990. We sought to determine the prevalence of, and factors associated with, hepatitis C (HCV), hepatitis B (HBV) and HIV infections among injecting drug users (IDUs) against this background. Design. Cross-sectional survey. Setting. Addiction treatment clinic. Participants. Seven hundred and thirty-five IDU tested for antibody to HCV (anti-HCV) between September 1992 and September 1997. Measurements. Socio-demographic and drug use characteristics. Serology tests for anti-HCV, HBV surface antigen (HBsAg) and HIV. Findings. The vast majority (89%) commenced injecting since 1990. Prevalence of anti-HCV was 61.8% (453/733), of HBsAg was 1.0% (7/729) and of HIV was 1.2% (7/600). Logistic regression analyses indicated that longer history of injecting and increased daily drug expenditure were the only independent variables associated with significantly increased risk of HCV. The only characteristic associated with increased prevalence of HBsAg was a history of injecting prior to 1990 (3.8%, 3/80). HIV prevalence was significantly higher when aged over 24 years (3.7%, 6/162), when injecting commenced prior to 1990 (6.3%, 4/64) and when injecting over 5 years (6.5%, 4/62). Conclusions. HIV prevalence has sustained a low level in this population. Interventions which aim to halt transmission of HCV are necessary and will need to target IDU very early in their injecting careers and also those at risk of commencing to inject.