An uncommon case of primary abdominal pregnancy that was detected after rapid resolution of OHSS is reported. A 27-years-old nulligravida woman underwent ovarian hyperstimulation with human menoposal gonadotrophin (hMG) at another clinic and was admitted to our hospital with severe OHSS. Intravenous fluid therapy, albumin supplementation, and abodminal paracentesis was performed. The patient's massive ascites rapidly resolved, and she was discharged from our hospital. However, 4 weeks later, at about the 8th gestational week, she was readmitted to our hospital because of strong suspicion of abdominal pregnancy. Ultrasonography revealed a gestational sac (GS) and fetus with heartbeat in Douglas' pouch and an emergency laparotomy was performed. Both fallopian tubes, both ovaries and the uterus were completely intact and the GS was found on the anterior surface of the rectum. After removing GS, the muscle layer and serosal layer of the rectum were repaired. No bowel complications developed, and the post operative course was uneventful. To our knowledge, this is the first report of this very rare variant of ectopic pregnancy complicated by OHSS.