Magnetic resonance imaging of a 14-year-old girl with abdominal pain and known vaginal agenesis revealed massive hematocolpos with a normal cervix and uterine body. Prior ultrasound of this area was significantly limited by bowel loops anterior to the retroflexed uterine body and cervix, which were displaced cephalad out of the pelvic inlet and were not seen. Magnetic resonance is the examination of choice in patients with symptomatic vaginal agenesis prior to surgical correction.