We report a case of a multicentric form of Castleman's disease (CD). A thoracic computerized tomography (CT) scan showed multiple mediastinal and bilateral axillary lymph nodes. Fluoro-18 fluoro deoxyglucose (F-18-FDG) positron emission tomography-PET/CT scan demonstrated increased F-18-FDG accumulation in multiple lymphatic regions and in bilateral pleural areas. The histopathological sampling of an excised left axillary lymph node revealed a multicentric form of CD, of an intermediate (mixed) cell type. The disease, its differential diagnosis and the diagnostic contribution of nuclear medicine imaging, are described.