The cutaneous porphyrias are disorders of heme biosynthesis in which excessive formation of porphyrins, secondary to partial enzyme deficiencies, produces photosensitization. There are five main types: porphyria cutanea tarda (PCT); variegate porphyria (VP); hereditary coproporphyria (HC); erythropoietic protoporphyria (EPP); and congenital erythropoietic porphyria (CEP). They can be differentiated by measuring heme precursors in urine, feces, erythrocytes, and plasma. VP, HC, EPP, and one form of PCT (type II) are autosomal dominant conditions with low clinical penetrance. The autosomal recessive prophyrias (CEP and homozygous counterparts of type II PCT, VP, and HC) are rare disorders. The skin lesions in PCT (the commonest cutaneous porphyria), VP, HC, and CEP are similar: mechanical fragility, subepidermal bullae, hypertrichosis, and pigmentation. EPP is characterized by acute photosensitivity without these lesions. Acute attacks of porphyria may occur in VP and HC but not in other cutaneous porphyrias. Liver disease is an uncommon, potentially fatal, complication of EPP. PCT is commonly associated with chronic liver disease, is often caused by alcohol and usually mild. PCT can be treated by repeated venesection to deplete iron stores or with low-dose chloroquine. Treatment of the other cutaneous porphyrias is largely symptomatic; accumulation of beta-carotene in the skin is particularly effective in EPP.