Chronic hepatitis C virus (HCV) infection is common and often results in slowly progressive liver disease. Although acute hepatitis C is now uncommon, most patients with acute infection have developed chronic hepatitis, and, therefore, the pool of infected patients is large. We used a modification of a previously described natural history model for HCV infection to project the number of cases of HCV infection, cirrhosis, and liver failure over the next 40 years. The model estimated the prevalence of HCV infection in the United States was 3.07 x 10(6) in 1993 (compared with an adjusted National Health and Nutrition Evaluation Survey (NHANES) III estimate of 2.8 to 3.5 x 10(6)). A gradual decline in the prevalence of infection should occur by year 2040 because of aging and natural deaths among the infected pool. However, as the duration of infection increases in the surviving cohort, the proportion with cirrhosis will increase from 16% to 32% by 2020 in an untreated population. Complications of cirrhosis also will increase dramatically over the next 20 years: hepatic decompensation (up 106%), hepatocellular carcinoma (up 81%), and liver-related deaths (up 180%). Although current treatment regimens eradicate HCV in over 50% of cases, many more patients would need to be treated to significantly impact disease progression. Identification and treatment of every case of HCV infection (with or without cirrhosis) would reduce the number of cases of decompensated cirrhosis by almost half after 20 years. Despite the declining incidence of acute HCV infection, chronic hepatitis C is common. The prevalence of cirrhosis and the incidence of its complications will increase over the next 10 to 20 years, because the duration of infection increases among those with chronic hepatitis C. These data emphasize the need for greater access to transplantation by expansion of the donor pool, increasing use of split livers and living donors, and novel options such as xenotransplantation.