With widespread use of antenatal ultrasound, an increasing number of urinary-tract lesions are being detected, and the clinician is called upon to make management decisions. Parenchymal lesions of the kidney pose a special challenge because of the associated risk of the occurrence of malignancy. A case of an antenatally-detected solid/cystic lesion of the kidney diagnosed as a congenital cystic mesoblastic nephroma following nephrectomy is presented and the issues involved in therapeutic decision-making are discussed.