We describe a male patient with Behcet's syndrome and Castleman's lymphadenopathy. He was affected by severe oral and genital ulcers, bilateral uveitis, necrotic purulent nodules on both hands. A CT scan of the mediastinum showed the presence of a mediastinal mass. On the basis of histological and immunohistological findings, a diagnosis of Castleman's disease, angiofollicular type, was formulated. The lymphadenopathy was unicentric. After the surgical excision of the mediastinal mass (January, 1989) until now, Behcet's syndrome is in complete remission with a low dosage of prednisone.