ObjectiveThe estimated incidence of rudimentary horn pregnancy is one in 76,000. It is a life-threatening entity with a 50% risk of uterine rupture. With advances in prenatal ultrasound in recent decades, there may be an opportunity to detect rudimentary horn pregnancy earlier, resulting in a lower incidence of maternal morbidity and mortality. Management is typically resection of the rudimentary horn and the ipsilateral fallopian tube by either laparotomy or laparoscopy. Case ReportHere, we present the case of a 22-year-old woman with a suspected ectopic pregnancy of 12 weeks' gestation. Ultrasound and magnetic resonance imaging were performed as preoperative evaluations. A definitive diagnosis was made during laparotomy, and resection of the rudimentary horn pregnancy was performed. ConclusionDiagnosis and management of rudimentary horn pregnancy remain a challenge. We should be alert to prenatal ultrasound with the intention of making an earlier diagnosis, thereby resulting in decreased maternal morbidity and mortality.