In a review of 44 infants with multicystic renal dysplasia diagnosed prenatally by ultrasonography, contralateral anomalies, bilateral disease and other non-urinary congenital anomalies were rare. In approximately two-thirds of infants the lesion was impalpable and in 2 cases involution had occurred prenatally. All but 5 were managed conservatively and without complications, and partial or complete involution of the lesion occurred in more than 50% during follow-up. It was concluded that the natural history of this anomaly is usually benign and that conservative management is advisable.