We report a case of persistent urogenital sinus with hydrocolpos and associated renal anomalies diagnosed prenatally at 30 weeks' gestation. The prenatal findings were confirmed on postnatal ultrasonography and genitogram with voiding urethrogram. The imaging features and a review of the literature are discussed. The possibility of hydrometrocolpos secondary to urogenital sinus should be considered on prenatal sonography in the presence of a presacral cystic mass with clear urine or turbid contents and a fluid-debris level (cervical or vaginal secretions). Because the prognosis and neonatal management of isolated hydrocolpos (which usually resolves spontaneously) differ greatly from those of hydrocolpos associated with a cloacal malformation, it is important to diagnose prenatally any associated anomalies in order to allow optimal postnatal management. Copyright © 2010 ISUOG. Published by John Wiley & Sons, Ltd.