To determine the histologic pattern of hepatitis C, 54 liver biopsy specimens from 45 patients with a clinicopathological diagnosis of hepatitis C were studied. All patients were seropositive for antibody to hepatitis C virus by second-generation testing. Both transfusion-related and sporadic cases were included. More than half the samples showed chronic hepatitis without cirrhosis, whereas 44% showed developing or fully established cirrhosis. A histological pattern of mild chronic hepatitis with portal lymphoid follicles and varying degrees of lobular activity was found in many of the patients. Lymphoid aggregates or follicles were seen in 78% of biopsy specimens, but aggregates, less prominent than in hepatitis C, were also seen in 14 of 27 samples (52%) from patients with hepatitis B. We conclude that a characteristic histological pattern exists in chronic hepatitis C, that this pattern is not always found and that prominent lymphoid follicles, though not unique to hepatitis C, provide a useful diagnostic clue.