Health care workers are at risk of acquiring blood-borne infections. To assess the risk of exposure to hepatitis B or C in the case of occupational blood exposure, we determined the seroprevalence of these infections in 466 patients admitted to a Copenhagen university hospital. Serological markers for hepatitis B or C were detected in 56 patients (12.0%). The seroprevalence of HBsAg and anti-HCV was 0.9% and 1.5% respectively. HCV RNA, indicating ongoing hepatitis C, was found in five of seven anti-HCV-positive patients by polymerase chain reaction. The serological findings had not previously been diagnosed in 4 of 10 potentially infectious patients and only 6 of 10 patients belonged to high-risk groups. In conclusion, health care workers should be aware of the potential the occupational risk of hepatitis B and C even in a low-prevalence country like Denmark. Management of health care workers after blood exposure should include serological testing for both hepatitis B and C. Strict adherence to universal precautions is recommended and vaccination against hepatitis B should be encouraged.