Hepatocellular carcinoma (HCC) is less common and occurs at a much older age in urban than in rural southern African Blacks. These differences may reflect differences in the etiology of the tumor in the two populations. The purpose of this study was to compare the hepatitis B virus (HBV) status of 150 HCC patients who were born and had lived all their lives in a rural environment with 158 patients who were born and brought up in a rural setting but then became urbanized. HBsAg and all markers of present or past HBV infection [HBsAg(+) or anti-HBc(+) or anti-HBs] were significantly less common in the urban patients when the two groups were considered as a whole (p less than 0.001 and p less than 0.05, respectively). However, because the rural patients were considerably younger (mean age 34.7 years; 66% less than 40 years of age) than in urban patients [mean age 50.9 years (p less than 0.0005), 19.0% less than 40 years of age (p less than 0.001)], an age-related analysis was performed. No significant difference in any HBV marker was found between rural and urban patients. The association between active HBV infection and HCC was similar in young patients, both rural and urban, and the prevalence of HBs antigenemia decreased in both groups with increasing age. We conclude that the differences in incidence and age of onset of HCC in rural and urban southern African Blacks cannot be attributable to differences in HBV status.