Hydrocolpos and hydrometrocolpos is a condition characterized by a cystic dilatation od the vagina and/or uterus with accumulation of fluid as a result of congenital vaginal obstructions. It can be of secretory or urinary types, the last one when a vagino-vesical communication develops such as a sinus or chloaca. Other causes are vaginal septum, imperforated hymen. Clinical Case: Ten day old newborn, 46 XX with genital virilization (Prader IV) confirmed as due to Congenital Adrenal Hyperplasia, sonogram showed dilated vagina with fluid content due to neonatal hydrocolpos. Conclusion: It is important to maintain a high index of suspicion when a female newborn shows urogenital sinus, chloaca, genital virilization or imperforated hymen, as well as a female newborn with an abdominal mass. Diagnostic test of choice is a sonogram. Evaluation must be completed by a multidisciplinary team, including urology, endocrinology and pediatric gynecology for optimal patient management.El Hidrocolpos e Hidrometrocolpos es una condición caracterizada por dilatación quística de la vagina y/o del útero, con acumulación de líquido como resultado de obstrucciones vaginales congénitas. Puede ser de tipo secretorio o urinario, este último ocurre cuando existe comunicación vagino-vesical, como en el seno urogenital o anomalía tipo cloaca. Otras causas son septo vaginal, himen imperforado, malformación tipo cloaca y senourogenital. Caso: Recién nacida de 10 días, 46 XX, con virilización de genitales grado IV de Prader, cuyo estudio confirmó una Hiperplasia Suprarrenal Congénita y cuya ecografía demostró una vagina dilatada con contenido liquido correspondiendo a un hidrocolpos neonatal.