Epidemiological histories from reported cases of viral hepatitis have been collected by state and local health departments and submitted to the Communicable Disease Center. This information provided data concerning 538 cases of transfusion-associated viral hepatitis during a one-year period. The incidence of transfusion-associated viral hepatitis appears to vary markedly. For 15 states, minimal rates range from 0.0 to 2.4 per 100,000 adult population. Blood was received by 97.1% of the 538 cases and was the only material administered to 90.5%. Single-unit transfusions accounted for 16.9% of all cases. The risk of hepatitis following transfusion of pooled plasma and fibrinogen appears to be appreciably higher than that attributable to whole blood. The over-all case fatality rate was 11.2% and was 5.5% among persons under 40.