Renal ultrasonography was performed on 69 children who had a preauricular sinus. Three children (4.3%) were found to have a significant renal anomaly. Two children had hydronephrosis secondary to vesicoureteric reflux. One patient with branchio-oto-renal syndrome had an absent left kidney and a hypoplastic right kidney associated with two dysplastic arteries. Renal anomalies were significantly more common in patients with a preauricular sinus than the 1 percent incidence of renal anomalies reported in the general population. We recommend that renal ultrasonography be performed on all children with a preauricular sinus.