Pelvic ultrasound has become very important in the diagnostic planning of utero-vaginal malformations. Having studies 93 congenital malformations of the utero-vaginal tract, the authors used ultrasound investigations as a first or second line of approach. They are able to describe the way ultrasound can be used for each type of malformation. Ultrasound is undeniably reliable for diagnosing bilateral incomplete aplasia of the uterus; so avoiding the need for laparoscopy. When failure of the uterus to develop on one side occurs it is possible to look for a closed or canalized rudimentary uterine nodule to confirm the diagnosis of a pseudo-unicorn uterus. The diagnosis by ultrasound of a bifid uterus shows up by the appearance of a "V" shape on the bladder. An intra-uterine septum can be diagnosed according to how serious the embryological abnormality is on ultrasound. Similarly the difference between a bicornuate uterus that is really just arcuate or partially septate cannot always be made with ultrasound because the embryological defect is a relatively minor one. Ultrasound examination is able to give a lot of information in diagnosing and calculating how much of the menstrual fluid is held back either on one side or completely. Its value is less when the two sides of the uterus communicate with one another. Although this way of examining patients may make it possible quite often to avoid carrying out hysterosalpingogram and laparoscopy, its greatest value is found when all methods of diagnosis are combined and interpreted in the context of a clinical situation.