BackgroundRudimentary horn pregnancy is a rare life-threatening obstetric condition with clinical and sonographic presentation resembling that of an abdominal pregnancy. Preoperative diagnosis of advanced rudimentary horn pregnancy is difficult and cases are often identified incidentally during laparotomy for a presumed abdominal pregnancy.Case presentationWe report a case of a 29-year-old African woman, gravida 2 para 1 at 28 weeks of gestation complaining of epigastric pain for 7 days with no other associated gastrointestinal or genitourinary symptoms. On examination, she had normal vital signs and an enlarged abdomen sized at 33 cm with unremarkable fetal lie and presentation. She had normal laboratory blood results with an ultrasound revealing an abdominal pregnancy of 28 weeks. The informed decision for conservative management was planned after informing of the benefit and risks of early termination versus conservative management, however, with worsening symptoms an emergency laparotomy had to be performed in which a left unruptured rudimentary horn pregnancy with a viable fetus was identified incidentally and delivery of the fetus followed by surgical excision of the horn was done. The postoperative period was uneventful, and the patient was discharged home with her newborn.ConclusionRudimentary horn pregnancy is very rare and often indistinguishable from an abdominal pregnancy in advanced gestation age. First trimester ultrasound is by far the only noninvasive sensitive diagnostic modality for rudimentary horn pregnancy. Laparotomy with horn excision remains the standard of care for advanced rudimentary horn pregnancy.