Porphyria, sometimes referred to by the obsolete term "hematoporphyrinuria," is a disease or a group of diseases associated with an intrinsic or inborn error of porphyrin metabolism. The three types recognized by most authorities are (1) congenital, (2) acute and (3) chronic. Almost all of the reported cases of porphyria have occurred in Europe, and the small number of papers in this country have dealt mainly with the acute type and, to a lesser extent, the congenital type. To our knowledge the only case of chronic porphyria which had been reported in this country proved to be a case of acute porphyria with mental symptoms; hence the object of recording this case. Nesbitt has suggested that porphyria is not as uncommon as is indicated by the paucity of case reports, and that if attention is focused on this disease more cases will be detected. The historical, chemical and clinical aspects