Castleman's disease is a rare disorder characterized by lymphoid hyperplasia. It may present as asymptomatic involvement of one lymph node group or as a multicentric disease with systemic features. We report a patient with Castleman's disease who presented with axillary lymphadenopathy associated with a solitary plasmacytoma originating from a rib. The affected rib was surgically resected and radical radiotherapy was subsequently administered to the axillary lymph nodes. In this particular case, a joint surgical and oncologic approach resulted in a successful outcome.