A RARE DISEASE: Paraneoplastic pemphigus is an rare autoimmune bullous skin disease recently recognized. About 50 cases have been reported since its first description in 1990.Clinical signs are polymorphous resembling the cutaneomucosal manifestations of pemphigus vulgar (skin and mucosa erosions, fragile interdermal bullae), pemphigoid (urticaria, distended subepidermal bullae), and polymorphous erythema (plaque lesions). Mucosal erosions predominate however.Most cancers associated with paraneoplastic pemphigus are hematologic diseases (non-Hodgkin's lymphomas, chronic lymphoid leukemia).No standard treatment has been defined. General corticosteroids and treatment of the causal disease are indicated. The clinical course of paraneoplastic pemphigus does not always follow the course of the associated neoplasm.Pathology criteria (keratinocyte necrosis, suprabasal keratinocyte vacuolization, intraepidermal acantholysis) and immunohistological findings (antibody and complement deposits at the dermo-epidermal junction and within the keratinocytes on different epithelial substrates) are insufficient for positive diagnosis. Autoantibodies must be identified by immunoprecipitation or immunoblotting to identify the target antigen complex plakin components (desmoplakin I and II, periplakin, envoplakin), the major pemphigoid antigen, desmoglein 3, and certain yet unidentified antigens with a molecular weight of 170 kD.Paraneoplastic pemphigus appears as a model autoimmune paraneoplastic disease. Its origin remains elusive. It has been hypothesized that tumor-induced inhibition of tolerance to certain antigens implicated in the keratinocyte junctional systems could be involved.