Multicystic kidneys are commonly diagnosed today due to the widespread use of prenatal ultrasound. Children with a multicystic kidney are at increased risk of contralateral renal abnormalities. We performed a voiding cystourethrogram on 65 children with a newly diagnosed multicystic kidney to determine the incidence of contralateral vesicoureteral reflux. Ten children (15%) with a multicystic kidney had contralateral vesicoureteral reflux, including 8 of 37 boys (22%) and 2 of 28 girls (7%). Contralateral reflux occurred in significantly more white (22%) than nonwhite (4%) patients (p < 0.001). Reflux was grade I in 2 children, II in 2, III in 2, IV in 1 and V in 3. All children were placed on antimicrobial prophylaxis. During a mean followup of 3.1 years grades I and II reflux resolved. Grade III reflux resolved in 1 child and remained stable in 1. Grade IV reflux was downgraded to III in 1 child on prophylaxis. One child with grade V reflux was stable on prophylaxis while the remaining 2 patients underwent ureteroneocystostomy. No child had a urinary tract infection. A significant proportion of white children with a multicystic kidney have contralateral vesicoureteral reflux and initial imaging should include a voiding cystourethrogram.