Castleman's disease is a rare, benign disease of unknown cause that induces reactive lymph node hyperplasia, most commonly in the mediastinum. It has 2 histologic subtypes: hyaline vascular and plasma cellular. A definitive diagnosis necessitates tissue biopsy. A specimen may be even misdiagnosed as lymphoma in frozen section. Surgery is the treatment of choice for the solitary form, whereas chemotherapy, radiotherapy, and steroids are proposed for the multicentric type. A neck mass diagnosed as Castleman's disease in a 48-year-old woman is reported.