The epidemiology and clinical outcome of hepatitis D viral infection in HBsAg-positive acute hepatitis, chronic liver disease, primary hepatocellular carcinoma and the symptomless carrier state was studied in Jordan. The prevalence of hepatitis D viral infection was significantly higher in patients with chronic liver disease (18/79, 23%) and acute hepatitis (17/108, 16%) than in symptomless HBsAg carriers (2/136, 2%). The highest prevalence of hepatitis D viral infection was found in patients with primary hepatocellular carcinoma (10/15, 67%) who were also significantly older than such patients without hepatitis D viral infection. Antihepatitis D virus IgM was detected persistently in 83% of patients with antihepatitis D virus-positive chronic liver disease and transiently in 41% of patients with acute hepatitis. A trend to increased mortality was observed in acute hepatitis D viral superinfection (25%) compared to hepatitis D viral coinfection (0%) and to antihepatitis D virus-negative HBsAg-positive acute hepatitis (4%). In patients with established chronic liver disease, however, neither survival nor histological parameters of disease activity were significantly different in the antihepatitis D virus-positive and antihepatitis D virus-negative groups. While the early stage of hepatitis D viral superinfection is associated with increased mortality, it appears that in patients with late-stage chronic liver disease, severe histological activity subsides, and survival is no longer influenced by the factor of hepatitis D viral infection. However, primary hepatocellular carcinoma appears to complicate the course of those antihepatitis D virus-positive patients surviving beyond this stage.