Pregnancy in rudimentary horn is an uncommon presentation of an ectopic pregnancy. It needs a very high degree of suspicion for diagnosis and the diagnosis becomes difficult in cases with previous vaginal deliveries. A 25-year-old female patient with two spontaneous vaginal deliveries and a history of spontaneous abortion at five months visited the obstetric emergency department with a history of five months of amenorrhea with pain abdomen and breathlessness for one day. On abdominal examination abdomen was distended, and rigid, and tenderness was present. Paracentesis was done where blood was present. On bimanual examination, cervical motion tenderness was present, and left-sided fornices fullness was present. The patient was admitted, and her sonography was done for suspicion of a ruptured uterus or ectopic pregnancy. The sonography report showed a bulky uterus with decidual reactions and a well-defined pregnancy of 21 weeks and 6 days in the right adnexal region with hemoperitoneum suggesting suspicion of ruptured ectopic pregnancy. After initial treatment and arrangement of two units of packed red blood cells after proper grouping and cross-matching for the patient, laparotomy was done. At the time of surgery, there was a right-sided rupture of non-communicating rudimentary horn pregnancy with a unicornuate uterus. A dead fetus of 600 grams lies in the peritoneal cavity with two liters of hemoperitoneum. Timely diagnosis and laparotomy saved the life of the patient.