Castleman disease is a relatively uncommon lymphoproliferative disorder. A presentation as an isolated lesion in the neck is extremely rare. We report the case of a 26-year-old man who presented with a 4-month history of an enlarging right neck mass that was identified as Castleman disease on excisional biopsy. The biopsy was curative. In localized forms of Castleman disease, excisional biopsy is both diagnostic and curative. However, in multicentric forms, additional treatment is required.