Background: The standard treatment for complex atypical hyperplasia is hysterectomy and bilateral salpingo-oophorectomy. Although radical surgery offers high survival prospects, it also eliminates any chance of further fertility, thus in young nulliparous women who wish to preserve their childbearing potential, a conservative progestin therapy is preferable. Case report: The authors report a case of complex atypical hyperplasia in a 29-year-old nulliparous woman with polycystic ovary syndrome treated with norethisterone acetate in order to preserve her childbearing potential. The specimens sampled during the follow-up demonstrated inactive endometrium with pseudodecidual changes and no ultrasonographic images exhibited abnormal endometrial thickness. Conclusion: According to literature and to the authors’ experience, they can affirm that progestin treatment is the most reasonable option for young nulliparous women affected by complex atypical hyperplasia who desire to maintain their fertility potential, showing its efficacy also in patients with an associated polycystic ovary syndrome.