Unilateral cervicovaginal agenesis in a didelphic uterus is an extremely rare congenital anomaly. Women born with this anomaly present with menarche associated with progressive dysmenorrhea and symptoms of worsening endometriosis. Presented here is a case of a 12 year old nulligravid who presented with progressive cyclic abdominal pain. Physical examination revealed a tender large right adnexal mass and presence of a vaginal canal and cervix tilted to the left. Sonography showed the presence of uterine didelphys, right hematosalpinx and hematocolpos. Preoperative impression was outflow tract obstruction probably due to Herlyn Werner-Wunderlich syndrome. However, intraoperatively, it was discovered this was a case of uterine didelphys with outflow tract obstruction of the right hemiuterus due to unilateral cervicovaginal agenesis and ipsilateral renal agenesis.