Many factors affect the development of the female reproductive tract. Obstructive anomalies prevent normal menstruation, allow for collection of blood in the uterus and the vagina, and may increase the incidence of retrograde menstruation. A high index of suspicion is necessary to diagnose these disorders, and an adequate workup is essential. This report will present a case of obstructive longitudinal vaginal septum. The workup and operative findings will be described, followed by a classification and discussion of other obstructive Müllerian anomalies. The incidence, workup, and management will be reviewed. (Am J Obstet Gynecol 2001;185:338–44.)