A 79-year-old Japanese woman presented with severe recalcitrant erosions on her oral mucosa, resembling paraneoplastic pemphigus. Using indirect immunofluorescence, we detected IgA antibodies against the cell surface, and both IgG and IgA antibodies against the basement membrane zone. Immunoblotting showed that the IgG antibodies reacted weakly with bullous pemphigoid 230 and periplakin, whereas the IgA antibodies did not react with any antigen. IgA antibodies to both desmoglein (Dsg)1 and Dsg3 were detected by ELISA. IgA antibodies to desmocollin (Dsc)3 were also detected by using cDNAs for human Dsc1–3 transfected into COS-7 cells. Despite treatment with oral prednisolone, high-dose intravenous immunoglobulin and double-filtration plasmapheresis, the skin lesions remained active, and the patient died from bronchiolitis obliterans-like respiratory failure. Despite extensive investigations and postmortem examination, no underlying neoplasms were found. The complex immunopathological findings probably played an important role in the development of the patient's unusual clinical features.