The following is a report of the unusual case of a multilocular cystic nephroma in an 8-year-old boy who was transferred to our unit with a palpable abdominal tumor. The patient suffered from thoracic pain and night sweating. The laboratory values were normal. Abdominal sonography showed a huge kidney tumor on the right side consisting of numerous small cysts transversed by irregular septa of variable thickness. The cysts had a diameter of 1 -5 mm; larger cysts of more than 1 cm in diameter were not able to be shown. In the center of the tumor a normal renal parenchyma was able to be shown. The tumor arose like a mushroom from the kidney. Color Doppler sonography showed good vascularity of the normal renal parenchyma while the tumor had only a few internal vessels. The tumor was surgically removed. The histologic diagnosis was cystic nephroma. Unusual features of this tumor were the small size of the numerous cysts similar to polycystic kidney disease and the mushroom-like growth of the tumor.