The porphyrias are a group of rare metabolic diseases that may present in childhood or adult life and are due to deficiencies of enzymes in the heme biosynthetic pathway. The most common manifestations are related to accumulation of intermediates in the pathway and usually occur as acute neurological attacks, or cutaneous photosensitivity. Multiple mutations have been identified in each of the porphyrias. The risk of disability or death from these disorders is significant, in part because diagnosis is often delayed due to lack of adoption of diagnostic testing in clinical practice. Moreover, the natural history of these disorders is not well described and it is not known what determines differences in outcomes. New therapies are needed. For existing therapies, high-quality evidence on short and long term efficacy and safety is generally lacking. Therefore, the purpose of this long-term follow-up study of a large group of patients with the various porphyrias is to provide a better understanding of the natural history of these disorders, as affected by available therapies, and to aid in developing new forms of treatment.