Psoriatic skin disease is common; it occurs at all ages and co-exists with joint disease in approximately 10% of cases. All areas of skin, scalp and nails may be involved. In the typical case, the skin lesions are easy to recognize. Atypical forms of skin involvement and lesions at unusual sites are less easily diagnosed by non-specialists. The cause is unknown, but there is a clear genetic element, with external factors being important in precipitation and exacerbations of the condition. Topical treatment is successful in most patients, but in resistant cases combinations of systemic therapy and ultraviolet radiation usually give good control. Although there is no cure, the majority of sufferers live normal lives and, with the exception of severe erythrodermic or generalized pustular psoriasis, there is no mortality. Morbidity, particularly social and occupational, is more of a problem than is often acknowledged.