Background: Ovarian hyperstimulation syndrome (OHSS) is a rare manifestation of functioning gonadotropinomas. Differential diagnosis and appropriate treatment improve the prognosis. Objective: To show a case of OHSS as a manifestation of FSH-producing pituitary adenoma. Case: We present a 21-year-old woman with visual and menstrual disturbances, a pituitary adenoma > 6 cm in diameter, FSH 40 mIU/ml, LH < 0.09 mIU/ml, oestradiol 974 pg/ml, PRL 90 ng/ml and bilateral ovarian size >12 cm. More than 90% of the adenoma was resected with pathological confirmation of gonadotropinoma, in the follow up without recovery of gonadal function. Conclusions: OHSS with a functioning gonadotropinoma is a rare entity that can occur in women in reproductive age. It should be approached comprehensively to achieve optimal results.