To investigate clinicopathologic characteristics of hepatocellular carcinoma (HCC) in young adults, excised tumors from 21 patients younger than 45 years (young group) were compared with findings in tumors from 204 patients older than 45 (old group). In the young group HCC showed (1) a high incidence of positive hepatitis B virus surface antigen (HBsAg) (young 71.4% versus old 20.1%); (2) relatively well-preserved hepatocellular function (indocyanine green test; young 10.7 +/- 8.8% versus old 20.6 +/- 10.8%); (3) low incidence of histologically verified concomitant cirrhosis (young 52.4% versus old 78.4%); and (4) a more advanced stage of the disease in TNM classification (Stage III; young 52.4% versus old 18.1%). With respect to survival rates achieved by surgery, there was no statistically significant difference between the two groups. Thus, hepatitis B virus may relate to the occurrence of HCC in the young patients. Despite the advanced stage in the young group, survival rate after surgery was comparable with that achieved in the old group. These observations mean that a close periodic surveillance of young adults with a positive HBsAg is required to detect HCC at an early stage. Treatment of patients with HBsAg using interferon or vidarabine and hepatitis B vaccine should be made to convert HBsAg to negative in these individuals.