Controversy exists as to what is the optimal management of antenatally detected multicystic dysplastic kidney disease (MCDK): conservative or operative. We report 70 (31M, 39F) children with unilateral MCDK in whom the initial micturating cystourethrography revealed vesicoureteric reflux into the contralateral kidney in 16/63 (25%). Involution of the MCDK kidney was noted at birth in 4 and occurred by 2 y of age in 11/46 (24%), with 16/46 (35%) showing a significant reduction in size. Of 21 children followed to 5 y, the MCDK had disappeared in 3 (14%) and 8 (38%) had shown a further reduction in size. No child has developed hypertension or proteinuria. Four children had urinary tract infections with lower tract symptoms, but no scarring of the normal hypertrophied kidney. We conclude that conservative management of unilateral MCDK is justified with long-term follow-up consisting of annual clinical review and ultrasound evaluation at 2, 5 and 10 y.