A unicornuate uterus with a rudimentary horn is a uterine anomaly resulting from the incomplete development of one of the Müllerian ducts and an incomplete fusion with the contralateral side. Pregnancy in a rudimentary horn is a rare condition that can lead to a catastrophic outcome when it ruptures. The majority of cases are diagnosed late. The use of ultrasonography helps clinicians to diagnose uterine malformations earlier, which can then be confirmed by a MRI or a laparoscopy. The standard treatment for a rudimentary horn pregnancy is surgical excision to prevent complications and recurrence.