BACKGROUND Retroperitoneal ectopic pregnancy (REP) is an extremely rare type of ectopic pregnancy, with a total of less than 20 cases reported in the English literature. However, failure to recognize REP may result in severe consequences. METHODS We report a case of 32-year-old woman with REP. She had amenorrhea, left lower abdominal pain, but no vaginal bleeding. Her urine human chorionic gonadotropin (HCG) test was positive and blood HCG level was 1880 m-international units per milliliter (mIU/mL). Transvaginal ultrasound sonography showed a left adnexal mass. Laparoscopy found an enlarged uterus, normal right uterine tube and ovary, and normal left uterine tube. The left ovary was partly covered by a blood clot, but appeared normal after removing the clot. There was a 10-mm circular peritoneal defect located lateral to the left sacrocervical ligament, anterior to the left ovarian fossa, and next to the lower edge of the left broad ligament. The patient was diagnosed of having REP with the gestational tissues covered by the peritoneum. The REP was removed by laparoscopic surgery. Bleeding was stopped by bipolar coagulation and absorbable hemostatic cellulose. The patient recovered smoothly and was discharged on the next day after surgery. Her blood HCG returned to normal range 29 days after surgery. CONCLUSIONS REP is very rare, but in any suspected case of ectopic pregnancy, caution must be paid to find signs of REP when the common sites of ectopic pregnancy do not have any positive findings.