Clinical observations have suggested that the number of cases of hepatocellular carcinoma has increased in the United States. We analyzed data from the Surveillance, Epidemiology, and End Results (SEER) data base to determine the age-adjusted incidence of hepatocellular carcinoma from 1976 to 1995, data from the U.S. vital-statistics data base to determine age-adjusted mortality rates from 1981 to 1995, and data from the Department of Veterans Affairs to determine age-adjusted rates of hospitalization for the disease from 1983 to 1997. The incidence of histologically proved hepatocellular carcinoma increased from 1.4 per 100,000 population (95 percent confidence interval, 1.3 to 1.4) for the period from 1976 to 1980 to 2.4 per 100,000 (95 percent confidence interval, 2.3 to 2.4) for the period from 1991 to 1995. Among black men, the incidence was 6.1 per 100,000 for the period from 1991 to 1995, and among white men, it was 2.8 per 100,000. There was a 41 percent increase in the mortality rate from primary liver cancer and a 46 percent increase in the proportion of hospitalizations attributable to this disease during the periods studied. The incidence increased significantly among younger persons (40 to 60 years old) during the period from 1991 to 1995 as compared with earlier periods. An increase in the number of cases of hepatocellular carcinoma has occurred in the United States over the past two decades. The age-specific incidence of this cancer has progressively shifted toward younger people.