Sixty-nine consecutive patients with acute type A hepatitis were followed-up to establish the natural history of the disease. Illicit drug abusers were not included in this study. 19% (13/69) of the patients at 6th month, and 6% (4/69) at 12th month showed aminotransferase (ALT) values at least two folds the upper levels. The histological examinations performed in 5 of these cases suggest that persistence of abnormal ALT levels may be related to a misdiagnosed chronic liver disease preexisting the acute type A hepatitis. Three of the 69 patients had a relapsing hepatitis with two peaks of serum ALT 6-8 weeks apart. The illness resolved uneventfully in all these patients. The exclusion of exposure to liver toxins such as alcohol or drugs, as well as other known hepatitis virus infection in these cases, suggests that the two distinct episodes of hepatitis could be the result of the sequential infection of hepatitis A and non-A, non-B viruses.