BACKGROUND: We present a rare case of pregnancy in a noncommunicating rudimentary horn that ruptured at 20 weeks. CASE: A 30-year-old woman presented with a history of two spontaneous abortions. An ultrasound scan showed a bicornuate uterus, with one normal and one hypoplastic horn. Hysterosalpingography revealed a single uterine cavity with only one tube, suggesting a unicornuate uterus. Hysteroscopy and laparoscopy were recommended but declined. She presented again 2 months later at 7 weeks’ gestation. A single intrauterine pregnancy in the hypoplastic right horn was diagnosed. A transvaginal scan showed a single cervical canal in continuity with the left uterine horn, which led to the suspicion of a pregnancy in a rudimentary horn. The option of pregnancy termination was offered. A laparoscopy was repeatedly suggested but declined. Excision of a ruptured noncommunicating rudimentary horn and ipsilateral salpingectomy were performed after an emergency laparotomy at 20 weeks because of the sudden onset of abdominal pain and signs of shock. CONCLUSION: Although a rudimentary horn pregnancy had been suspected before the laparotomy, the patient presented as a clinical emergency. This report, like others, indicates that prompt diagnosis and immediate removal of the rudimentary horn is lifesaving.