Forty-seven drug addicts with histologically verified chronic non-A, non-B hepatitis were followed up for at least 12 months (mean 58 +/- 34.5 months). The patients were young, mean age 25 years and predominantly of the male sex. Forty patients (85%) had chronic persistent hepatitis (CPH) in the first biopsy and seven (15%) had chronic active hepatitis with or without cirrhosis (CAH/C). Except for bilirubin levels, standard biochemical tests at the time of the biopsy did not differ significantly between the two histologic groups. Ten patients had repeated biopsies performed and in four of them a histologic progression was observed. Six patients with CAH had evidence of cirrhosis. No patient developed hepatic failure or died because of the liver disease. Two patients seemed to resolve biochemically during follow-up. The rather benign liver morphology contrasts with chronic NANBH after blood transfusion where chronic active hepatitis and cirrhosis are much more common. Age-dependent immunologic factors might to some extent explain these differences.