Objective : Uterus didelphys with hemivaginal obstruction, unilateral renal agenesis, known as Herlyn-Werner-Wunderlich syndrome(HWW syndrome), is rare congenital anomaly.We'd like to present transabdominal and transvaginal ultrasonographic findings of Herlyn-Werner-Wunderlich syndrome. Method : From March 2003 to December 2008, 5 cases of HWW syndrome were diagnosed with ultrasonography and pelvic MRI. Transabdominal and transvaginal sonography were retrospectively reviewed and correlated with MRI and CT. Results : All the five patients complained cyclic lower abdominal or pelvic pain during menstruation. Two of five patients underwent follow up ultrasound examinations and pelvic MRIs in different period of menstrual cycle. Fluid retention within vaginal canal was most frequent ultrasound findings(four out of five patients, 6 out of 7 ultrasound examinations). Endometrial fluid collection were visualized in only two patients, and one of them revealed resolution of hematometra on follow up ultrasound examination. One patients who had a pin-point hole in vaginal septum showed no definite fluid in vaginal canal. Salphingeal dilatations were not seen even in patients with hematometra. Pelvic MRI had advantage in visualization of ectopic atretic ureter in two cases. Conclusion : Hematocolpos was the most common ultrasound finding of Herlyn-Werner-Wunderlilch syndrome and hematometra could be transient findings, so vaginal flulid retention in patients with uterus didelphys with unilateral renal agenesis suggest possibility of Herlyn-Werner-Wunderlich syndrome.