Ectopic pregnancy is considered as a possible diagnosis in cases in which women experience acute abdominal pain and a urinary human chorionic gonadotropin (hCG) test produces a positive result. However, we present a case of ruptured ectopic pregnancy involving a negative urinary pregnancy test result. A 34-year-old nulliparous woman was admitted to the emergency room of our hospital due to the sudden onset of lower abdominal pain. Rebound pain in the lower abdomen was detected during a physical examination. Since transabdominal ultrasonography showed massive ascites, and a urinary pregnancy test produced a negative result, we performed a contrast-enhanced computed tomography scan and found a 5-cm right-sided ovarian cyst and extravasation around the left adnexa. We diagnosed the patient with left ovarian hemorrhaging and a right ovarian hemorrhagic luteal cyst. Two hours later, hemorrhagic shock occurred, and an emergency laparoscopic operation was carried out. We detected a swollen left fallopian tube, which had ruptured and was bleeding. We performed left salpingectomy. After the operation, the patient's preoperative serum sample was re-examined to re-assess her hCG level. As a result, her serum hCG level was found to be 23.3 mIU/ml. Pathological examinations showed a very small number of chorionic villi. The final diagnosis was ectopic pregnancy. The patient's postoperative course was uneventful. This case report illustrates the difficulty of diagnosing ectopic pregnancy. Clinicians should include ectopic pregnancy in the differential diagnoses for cases of acute abdominal pain involving women of reproductive age, regardless of the results of urinary pregnancy tests.