Health-care workers have an occupational risk of infection with hepatitis C virus (HCV). However, neither the magnitude of this risk nor the practices associated with it have been defined. Since dentists have numerous patients and are exposed to blood, they are likely to have the maximum risk. Therefore, we have assessed occupational risk for HCV infection among dentists in the New York City area. Individuals who admitted present or previous intravenous drug use or (men) who were homosexual or bisexual were excluded. Demographic, occupational, and behavioural data were recorded, and sera were tested for antibodies to HCV (anti-HCV). Anti-HCV was found in 8 (1.75%) of 456 dentists compared with 1 (0.14%) of 723 controls (odds ratio [OR] 12.9, 95% confidence interval [CI] 1.7 to 573). Anti-HCV was found in 4 (9.3%) of 43 oral surgeons compared with 4 (0.97%) of 413 other dentists (OR 10.5, 95% CI 1.9 to 58). Seropositive dentists claimed to have treated more intravenous drug users in the week (p = 0.04) or month (p = 0.03) before the study than did seronegative dentists. Our findings show that dentists are at increased risk for hepatitis C infection. All health-care workers should regard patients as potentially infected with a communicable bloodborne agent.