A 70-year-old patient presented erosions on the oral mucosa and skin, predominantly in perianal and inguinal areas. Histopathologically, subepidermal blistering was observed. By direct immunofluorescence microscopy, linear deposits of IgG and C(3) were seen at the dermal-epidermal junction. By indirect immunofluorescence microscopy, binding of IgG autoantibodies to the dermal side of NaCl-split skin was detected. These autoantibodies were shown to target both the non-processed and processed alpha(3)- as well as the beta(3)-subunit of laminin 5 by immunoblot analysis using extracellular matrix of cultured human keratinocytes. Based on these results, the diagnosis of an anti-laminin 5 mucous membrane pemphigoid was established. Oral treatment with dapsone, combined with intravenous dexamethasone pulse therapy, led to rapid improvement.