A variety of cutaneous adverse reactions, leading from mild maculo-papular rashes to life-threatening conditions, may be caused by drugs. Erythroderma, exfoliative dermatitis, and acute generalized exanthematic pustulosis as well as blistering diseases such as pemphigus vulgaris, bullous pemphigoid, generalized bullous fixed drug eruption, Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are often drug-induced. In general, SJS and TEN are considered as severe skin reactions within the spectrum of erythema multiforme. Histopathologically severe skin reactions present with necrotic keratinocytes either in wide dissemination or full-thickness necrosis of the epidermis. Vacuolization leading to subepidermal blistering is seen in the basal membrane zone. A superficial, often perivascular, lymphohistiocytic infiltrate can be seen in the upper dermis. In order to clarify these problems and also to further investigate the confounding or interaction of infection and antiinfective treatment, the European case-control surveillance of severe cutaneous adverse reactions called EuroSCAR was started in March 1997.