To report the occurrence of a rare case of spontaneous ovarian hyperstimulation syndrome in a naturally conceived singleton pregnancy.A case report.The Obstetric and Gynecology Department at King Fahd Central Hospital, Jazan City, Saudi Arabia.Our reported case was a middle-aged Egyptian woman presented in the second trimester of her first pregnancy with persistent abdominal pains, shortness of breath, vomiting, and diarrhea.The data were collected by full history taking, clinical examination, transabdominal ultrasonographic examination, and by revision of results of the patient's laboratory tests.The possible event of spontaneous ovarian hyperstimulation syndrome in a naturally conceived singleton pregnancy.Our case was reported as a severe case of spontaneous ovarian hyperstimulation syndrome in a naturally conceived singleton pregnancy.This case report emphasizes the importance of thorough evaluation of all women presented with acute abdomen and ovarian masses during pregnancy. Although the condition is extremely rare, it is a potentially lethal in its severe form if not timely diagnosed and managed conservatively. With the increasing awareness of these conditions, more and more cases could be detected and reported.