Castleman disease (CD) is a rare lymphoproliferative disorder, the etiology and pathogenesis of which is not clearly established. It presents more commonly as a localised disease or unicentric CD (UCD), and less often as generalised disease or multricentric CD (MCD). The most common site of UCD is in the thorax; however, UCD is rarely included in the differential diagnosis of an intrathoracic mass due to its rarity. The lesion is highly vascular and often has dense adhesions with adjacent organs, making the surgery a difficult task. We report a case of posterior mediastinal mass located in left paraspinal region which was detected incidentally in a 53-year old female and was subsequently resected successfully via left postero-lateral thoracotomy, and was diagnosed post-operatively on histopathological examination (HPE) as CD, hyaline vascular variant (HVV). We review the relevant clinical, pathological and radiological findings of CD, which may act as clinical pointers for establishing a preoperative diagnosis of CD. Suspecting CD preoperatively would guide the surgeon for appropriate surgical planning and may avoid facing such surprise on the operating table.