Mature Cystic Teratoma of Renal Pelvis: An Unusual Presentation at an Uncommon Site.

Teratoma of the kidney is uncommon. We report a case of a young boy with a large, right-sided retroperitoneal cyst suspected as lymphangioma causing hydronephrosis. His renal pelvis was dilated, containing purulent fluid, and a nephrectomy was performed.