BACKGROUND: McCune-Albright syndrome (MAS), due to a somatic mutation of the GNAS1 gene, begins usually in girls with peripheral precocious puberty. Ovarian autonomy may persist in adulthood with acyclic hyperestrogenemia, infertility, and a potential risk of estrogen-dependent cancer. CASE: A 22-year-old woman, with MAS, was referred for infertility with left macropolycystic ovary, hyperestrogenemia, and chronic anovulation unsuccessfully treated by controlled hyperstimulation. Once ovarian cyst punctures and cDNA analysis verified that GNAS1 mutation was restricted to the left ovary, unilateral ovariectomy was performed. It improved right ovarian function, allowed an in vitro fertilization-induced pregnancy, but revealed an unexpected borderline epithelial ovarian tumor. SUMMARY AND CONCLUSION: Several breast cancers have already been reported in young MAS patients but not a borderline epithelial ovarian tumor. In this context, we would recommend that persistent hyperestrogenemia in an adult be corrected and gynecological follow-up of the breasts, ovaries, and endometrium be implemented.