A group of 295 adult male patients from Cairo, Egypt, with acute hepatitis were studied. Acute hepatitis A was diagnosed in 8 patients (2.7%), hepatitis B in 115 (38.9%), delta infection in 19 (6.4%) and possible Epstein-Barr virus or cytomegalovirus-mediated hepatitis in 7 patients (2.4%). The remaining 146 patients (49.5%) were considered to have hepatitis non-A non-B. The clinical presentation of the various causes of hepatitis was similar, although patients with hepatitis B and delta infection had significantly higher mean alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels than patients diagnosed as having hepatitis non-A non-B. Various risk factors for the acquisition of hepatitis were evaluated. A history of an injection for medical treatment and a history of anti-schistosomal therapy were significantly associated with delta infection when compared to patients with either hepatitis B or non-A non-B (P less than 0.05). Hepatitis non-A non-B is a major cause of acute hepatitis in adults living in Cairo, and an iatrogenic source of infection may be important in the epidemiology of delta infection.