Castleman's disease or pseudo-tumoral lymphoid hyperplasia is a rare entity. We report a case of Castleman's tumour in the antero-superior mediastinum which was revealed by a radiological examination in a young woman of 26. We also report immunohistochemical studies. There are two clinical presentations of Castleman's disease; a localised form (mediastinal or extrathoracic) and the multicentric variety. The localised form may be asymptomatic or can be accompanied by general features of inflammatory disease. Surgical excision of these localised forms both confirms the diagnosis and assures a cure. The multicentric variety has various clinical peculiarities (the patients are older and/or immunosuppressed and suffering from multiple enlarged glands also in the viscera) and the disease in above all progressive. There are associations with Kaposi sarcoma and lymphoproliferative complications are described in this multicentric form and their prognosis remains poor.