We present a case of paraneoplastic pemphigus associated with Castleman's disease. Our patient had stomatitis and vulvar erosions followed by a cutaneous polymorphous eruption. Investigations for neoplasia disclosed a Castleman's tumour suggesting the diagnosis of paraneoplastic pemphigus. The diagnosis was supported by immunoblotting using an extract of cow tongue although keratinocytes extracts did not identify relevant target antigens. One year after surgical excision of the tumour the patient remained unwell with persistent buccal erosions and lymphopenia. This case is unusual because of the length of its evolution before the discovery of the Castleman's tumour. It is only the second occasion that the association between paraneoplastic pemphigus and Castleman's tumour has been reported. Our case emphasizes the usefulness of immunoblotting on cow tongue in suspected cases of paraneoplastic pemphigus.