Castleman disease (CD) is a rare lymphoproliferative disorder of unknown aetiology. It manifests in two distinct clinical presentations: unicentric and multicentric. Unicentric CD is rare and may present as an isolated neck mass. A 22-year-old man presented with a 6-month history of right neck swelling that occupied the posterior triangle of the right neck region. After surgical exploration, a solitary, well defined, and hyper vascular mass was excise. A histopathological examination confirmed the lesion as CD, hyaline-vascular variant. CD of the neck is a diagnosis that is usually not taken into consideration while evaluating neck masses due to its rarity and unassuming presentation. It should be keep in the differential diagnosis of neck masses as the clinical and radiological features evade a firm diagnosis. The treatment of unicentric CD is complete surgical excision, which cures the patient.