We investigated clinical characteristics and incidence of patients with acute non-A-G hepatitis, who were all registered in 17 Japanese National Hospitals. Seven hundreds thirty-one (24.0%) of 3052 patients with sporadic acute hepatitis and 73 (21.2%) of 344 patients with posttransfusion acute hepatitis were diagnosed as acute non-ABC hepatitis. Patients with acute non-ABC hepatitis were older (Mean +/- SD, 44 +/- 15 years) and male/female ratio was 0.70. Although mean levels of liver function abnormality was generally mild, 4(1.8%) of 250 patients with acute non-ABC hepatitis were died of fulminant hepatitis.