Psoriasis is a skin disease typically presenting with sharply demarcated, inflammatory, erythematous plaques with characteristic silver-white scaling due to epidermal hyperproliferation and parakeratosis secondary to the inflammation. The name derives from pisigmaomicronrhoalpha (mange or scabies), and in ancient times the disease was confused with leprosy resulting in expulsion from society. Hence, both itching and social stigmatization are major problems affecting patients with psoriasis. Today, psoriasis is recognized as a genetically determined, autoimmune, T cell mediated systemic disease manifesting on the skin, nails and joints and associated with a number of co-morbidities. Accordingly, therapeutic strategies are antiinflammatory, antiproliferative and keratolytic. The extent and severity of disease (PASI), impairment of life quality (DLQI), and affected anatomic regions (inverse, palmoplantar, nails) as well as co-morbidities (arthritis, metabolic syndrome, cardiovascular disease, depression) determine the therapy. In 80 % of cases psoriasis is mild or moderate and sufficiently treated with topical corticosteroids, vitamin D-analogues, and phototherapy. 20 % of patients suffer from severe psoriasis, necessitating systemic drugs such as acitretin, methotrexate, ciclosporin A or the newer biologic agents. Especially in severe psoriasis, psychological strain, co-morbidities, and medico-economic aspects must be taken into account.