Castleman's disease is an idiopathic lymphoproliferative disorder characterized by massive enlargement of lymph nodes. It may have a unifocal or multifocal presentation; the mediastinum is the most common site (70%). Patients with cervical disease usually have unifocal involvement (90%). The main problem posed by cervical Castleman's disease is that it should be considered in the differential diagnosis of cervical tumors. This report describes a patient who had unifocal Castleman's disease on the left side of the neck, and discusses the differential diagnosis with findings on magnetic resonance imaging, computed tomography and ultrasonography.