An association between two types of acute hepatic porphyria (porphyria variegata and acute intermittent porphyria) and hepatocellular carcinoma has previously been reported. In these studies, etiological factors for hepatocellular carcinoma were not completely sought. We report here the first case of an association between hepatocellular carcinoma and hereditary coproporphyria, the third type of acute hepatic porphyria. A 58-yr-old woman with hereditary coproporphyria presented with a 3.5-cm-diameter hepatocellular carcinoma. Results of exhaustive investigation of etiological factors for hepatocellular carcinoma were negative. Results of microscopic histological analysis of the nontumorous liver were normal. Five years after surgical resection, the patient had no evidence of tumor recurrence.