An unusual case is reported of the rare Castleman's disease localized in the retroperitoneal area in an elderly asymptomatic patient. A similar benign lymphoadenopathy of unknown etiology is generally found in the mediastinum and interests just one lymph-node that results abnormally hyperplastic. Histologically, most cases are of the hyaline-vascular type and much more rarely of the plasmacell variant. After a careful review of the literature the anatomical, pathological and clinical characteristics, the main etiopathogenetics hypotheses and diagnostic criteria are explained. The particular size of the neoformation is emphasized and also the impossibility to reach a correct preoperatory diagnosis owing to a suspect kidney parenchyma infiltration observed by RM. Also the intraoperatory report seemed to confirm the diagnostic hypothesis of a malign neoplasm infiltrating the lower pole of the kidney and which necessitated the total ablation of the retroperitoneal mass and left kidney. We concluded that the case which we have observed (the 32nd in world literature dealing with the retroperitoneal space) is not really comparable to those previously described by other authors. In fact the histopathological picture presents a series of ialino-vascular and plasmacell aspects which make any hypothesis of etiopathogenetic uncertain.