An elderly woman was found to have hepatocellular carcinoma and, incidental to this, markedly elevated levels of porphobilinogen in urine and serum. The delta-aminolevulinic acid levels in urine and serum were normal, but there was a distinct increase of porphyrins in urine and feces. Neither the patient nor her family gave a history suggestive of a clinical porphyria. The patient died from the carcinoma without ever exhibiting porphyric symptoms. It is assumed that the hepatocellular carcinoma produced the excessive amounts of porphobilinogen.