A follow-up liver biopsy was done 9-16 years (mean 12 years) after initial biopsy in 20 untreated Swedish patients infected with hepatitis C (8 men, 12 women; mean age 30 years at initial biopsy) in whom first biopsy had been classified as chronic persistent hepatitis. A significant progression of liver damage was found when using Histology Activity Index (HAI) scoring according to Knodell (p=0.006 for total HAI score; p=0.03 for grading, i.e., sum of HAI components 1, 2, and 3; p=0.01 for staging, i.e., HAI component 4, fibrosis). Fourteen of 20 (70%) patients had increased while 6 had decreased or unchanged HAI scores on follow-up biopsy. Occasional heavy alcohol drinkers (n=6) had an increased follow-up HAI score as compared with nondrinkers (p<0.05). Eight of 14 who deteriorated on follow-up versus 0 of 6 with improved or unchanged liver histology were anti-HBc positive (p=0.04). There was no significant correlation between HCV genotype and prognosis; however, the only two patients with liver cirrhosis on follow-up had genotype 1b. In conclusion, most patients with minimal or mild chronic hepatitis C in the present study had histologic progression on the latest biopsy. Cofactors such as alcohol abuse and exposure to hepatitis B may have a greater influence than HCV alone in determining the rate of deterioration of liver disease.