Castleman's disease is a rare nonclonal proliferative disorder of the lymph nodes with an unknown etiology. Common locations of Castleman's disease are mediastinum, neck, axilla, and abdomen. Castleman's disease of a peripancreatic location masquerading as pancreatic neoplasm is an even rarer entity. On search of published data, we came across about 17 cases published on peripancreatic Castleman's disease until now. Here we are reporting a case of retropancreatic Castleman's disease masquerading as retroperitoneal neoplasm in a 46-year-old male patient.