1. 1. Congenital hydrocolpos is caused by a combination of vaginal obstruction and fetal cervical gland secretion caused by stimulus of the maternal hormones. 2. 2. The vaginal obstruction may be caused by atresia, imperforate hymen, or possibly by a congenital fold of tissue which causes a valvelike obstruction in a partially stenotic vagina. 3. 3. The most important factor in treatment of this anomaly is the establishment of a correct preoperative diagnosis. 4. 4. When the correct diagnosis is made, most of these patients will be cured by a relatively simple transperineal drainage procedure. 5. 5. Long-term follow-up is essential since the distended, hypertrophic vagina and the associated hydronephrosis tend to develop intercurrent infection during their slow return to normal.