One-hundred nineteen patients (cases) at least 13 years of age with acute hepatitis were studied to determine the viral etiology of acute hepatitis in Omdurman, Sudan. Ninety-eight control subjects (controls) were also evaluated to determine the risk factors associated with the development of clinical disease. Acute hepatitis non-A, non-B was diagnosed in 88 cases (73.9%), hepatitis B in 15 cases (12.6%), delta infection in 15 (12.6%), and hepatitis A in just one patient (0.8%). A higher percentage of hepatitis B cases had received a parenteral injection for medical therapy during the previous 6 months than control subjects (26.7% vs 4.1%, p less than 0.05). The data in this study indicate that hepatitis non-a, non-B may be the major cause of acute hepatitis in adults in this area of Sudan. The suggested association of parenteral therapy with the transmission of hepatitis B could have important implications for the spread of other parenterally-transmitted diseases.