Background: Sanitary and socioeconomic changes and the identification of new causative virus, have changed the epidemiology of hepatitis in Chile. Aim: To study the natural history of acute hepatitis caused by virus A, E and non A-E in Chilean adults. Patients and methods: A special study protocol was followed for patients with a clinical picture of acute hepatitis. Anti HAV IgM, anti HBc IgM, anti HEV IgG and IgM and Anti HCV antibodies were determined by ELISA. Results: Fifty nine patients (30 male), aged 15 to 58 years old were studied. Eighty nine percent had jaundice and 50 to 70% had malaise and abdominal pain. Virus A was positive in 80%, virus E in 7%. In 14% of patients, all viral markers were negative. The evolution was typical in 78%, biphasic in 14% and cholestatic in 5%. One patient had a prolonged and one a fulminant course. Mean ALT was 1148 U/l and mean total bilirubin was 5.5 mg/dl. Seventy three percent of cases occurred during early winter and spring and 27% during summer and early autumm. Conclusions: The main etiology of acute viral hepatitis in Chile is virus A and most cases occur during the rainy season. Clinical features of hepatitis non A-E are similar to enteral transmission forms. (Rev Méd Chile 2001; 129: 523-30)