Cervical incompetence is basically a cervix that is too weak to stay closed during a pregnancy. It is generally categorized as premature opening of the cervix without labor or contractions.To estimate the incidence of incompetence of the uterine cervix at patients with congenital uterine malformations.Our study was a retrospective and prospective one between 2002 and 2009. We evaluate the length of the cervix by transvaginal ultrasonography during the second trimester of pregnancy.We had 316 cases with congenital uterine malformations. From these we found 49 (15.3%) women with incompetence of the cervix: 8 (2.5%) with unicornuate uterus, 11 (3.4%) with bicornuate uterus and 30 (9.5%) cases uterus with septum. For all these wad made cerclage when we found funneling of the cervix or the cervix was open less than 4 cm. The use of ultrasonography has been very helpful with the diagnosis, and is made when the cervical os (opening) is greater than 2.5 cm, or the length has shortened to less than 20 mm. All patients had preterm delivery.When we have cases with congenital uterine malformations we must think that incompetence of the cervix could be associated, so we must assess the status of the cervix for these patients by serial ultrasound examinations starting between 16 and 20 weeks of gestation. Our patients had preterm delivery caused not only the incompetent cervix, but the malformation of the uterus is implicated also.