Over the past 10 years, 12,146 cases of hepatitis were diagnosed in the Virology Department of Vienna University. 30.3% were hepatitis A, 39.2% hepatitis B, 3.0% cytomegalovirus and 1.5% Epstein-Barr virus infections. The remaining 25.8% were diagnosed as non-A, non-B hepatitis (NANB). Therefrom, a sample of 167 sera from acute and 78 from chronic hepatitis NANB were tested for hepatitis C. 9.6% of the acute and 44.9% of the chronic cases were positive. We conclude from these data that about 12% of all hepatitis cases in Austria are caused by the hepatitis C virus. In addition, risk groups for hepatitis C were tested. The highest prevalence (80%) was found in drug addicts. Polytransfused (organ transplanted) patients had antibodies in 44.8% of cases. Of 78 dialysis patients, 7 were positive but nearly all positives came from one single dialysis unit, thus indicating a prevalence of 30% there.