Porphyrias are a group of disorders caused by inherited deficiencies in the activities of the enzymes of the heme biosynthetic pathway. Afflicted patients suffer either from neurological disturbances, cutaneous photosensitivity, or both. The first recorded case of porphyria in Japan was a patient with congenital erythropoietic porphyria (CEP), and was reported by Sato and Takahashi in 1920. Since then, 884 cases of porphyria have been diagnosed based on characteristic clinical and/or laboratory findings (502 males, and 375 females and 7 of unknown gender). The most recent data available is dated December 31, 2007. We analyzed these 884 cases on the basis of chronological occurance, age distribution, gender difference, geographical distribution, risk factors, initial diagnosis of acute porphyric patients, and prognosis. In this study, we discuss our findings and will also explain the difficulties in gathering reliable data for accurate epidemiological research.