Paraneoplastic pemphigus (PP) is an autoimmune disease, which is frequently associated with non-Hodgkin's lymphoma. Autoantibodies against components of the cytoplasmic plaque of epithelial desmosomes are usually present in the sera and are believed to play a major pathogenic part in acantholysis and suprabasal epidermal blistering. However, another typical histological feature of PP, interface dermatitis with keratinocyte dyskeratosis, is shared with skin diseases that involve epithelial damage mediated by T cells. Here, we present the detailed characterization of the cutaneous T-cell response in a patient with PP and demonstrate a selective epidermal accumulation of activated CD8+ T cells together with an increased local production of interferon-gamma and tumour necrosis factor-alpha, and a strong expression of HLA-DR and ICAM-1 on keratinocytes. Apoptosis was identified as a key mechanism of keratinocyte death, and appeared independent of the FAS/FAS ligand (FAS-L) pathway, as epidermal expression of FAS was not increased compared with normal skin, and FAS-L was undetectable on the protein and mRNA level. Triple therapy with high-dose corticosteroids, cyclophosphamide and intravenous immunoglobulins reduced levels of pemphigus-like autoantibodies and reversed the cutaneous inflammatory reaction leading to long-standing clinical remission. Our findings support the concept of a major contribution of cytotoxic T lymphocytes to the immunopathology of paraneoplastic pemphigus.