The risk of hepatocellular carcinoma (HCC) and other internal malignancies was examined in patients with genetic hemochromatosis (GH) by following 208 patients from the time of diagnosis to June 1983 and by comparing the numbers of cancers they developed with expected values constructed from cancer registry incidence data by means of actuarial methods. In addition, cancers occurring in a comparison group of 148 subjects with other chronic nonalcoholic liver diseases (CLD) were determined. Among the GH group, 16 new cases of HCC occurred subsequent to the diagnosis of GH, together with 8 other malignancies. The 16 cases of HCC reflect a 200-fold excess risk, which from all indications represents the first quantitation of the risk of this tumor in GH. There appears to be no increased risk of other malignancies in this disease. Among the CLD group only 1 HCC and 1 other malignancy occurred.