Background: Peripheral precocious puberty (PPP) is defined as the early pubertal maturation independent of gonadotropin stimulation. Autonomous ovarian cysts can be a cause of PPP or isolated precocious menarche. The differential diagnosis of ovarian cysts is important because of distinct management options. Case presentaion: A 9 7/12-year-old girl presented because of rapid evolution of breast development and premature menarche. Estrogen levels were elevated while GnRH stimulation test revealed a blunt response. Pelvic sonogram demonstrated an ovarian cyst. She was started on oral letrozole. There was no further episode of menstruation. The cyst resolved spontaneously after three months. Conclusion:Functional ovarian cysts usually regress spontaneously. This case highlights the effectiveness of letrozole therapy in promptly decreasing estrogen levels and immediately controlling menstrual bleeding.