HighlightsSpontaneous ovarian hyperstimulation syndrome (OHSS) can result from hyperstimulation of the follicle-stimulating hormone (FSH) receptor by FSH or other glycoprotein hormones such as chorionic gonadotrophin hormone (hCG), thyroid-stimulating hormone (TSH), and luteinizing hormone (LH); mutations of the FSH receptor gene can make these receptors abnormally sensitive to hCG, TSH, or both.In patients with ovarian cysts and suspected spontaneous OHSS, it is important to determine whether hydatidiform mole, multiple pregnancie, hypothyroidism, glycoprotein-secreting adenoma or FSH receptor mutation are present.Although rare, in the context of spontaneous OHSS and abdominal pain, ovarian complications such as follicular rupture, cyst hemorrhage, or ovarian torsion should always be considered.