Castleman's disease is a rare lymphoproliferative disorder that is easily misdiagnosed. When it occurs in the head/neck and thorax, it can pose a diagnostic dilemma because of its lack of any specific presenting characteristics and distinguishing radiographic features. An accurate histopathologic diagnosis and careful staging are crucial to planning treatment. The highly vascular nature of the tumor makes surgical management challenging, and it warrants preoperative embolization whenever possible. We report 3 cases of Castleman's disease that involved the head/neck and thorax. We also review the presenting clinical features of Castleman's disease, its histopathologic characteristics, and the diagnostic and treatment challenges that it poses.