BACKGROUND This review is aimed at presenting classification and diagnosis criteria of hepatic porphyrias and at proposing guidelines for diagnosis and management of these diseases. BACKGROUND Porphyrias are inherited disorders: each type of porphyria is the result of a specific decrease in the activity of one of the enzymes of heme biosynthesis. Porphyrias are presently classified as erythropoietic or hepatic, depending on the primary organ in which excess production of porphyrins or precursors takes place. From 1970 to 1998, there have been important advances in the understanding of these diseases: specific enzyme deficiencies have been demonstrated, and genes have been isolated and located. These advances have been followed rapidly by identification of mutations. CONCLUSIONS Treatment of acute attacks by hematin completely changed the disease prognosis. Relationships between porphyria cutanea tarda and hepatitis C virus or hemochromatosis have also been clarified. However, several important issues are still not solved: for instance, pathogenesis of neuronal dysfunction that produces the acute attacks is poorly understood. Differences related to susceptibility to develop acute attacks are not known.