Objective In women with endometrial hyperplasia or stage 1A cancer, fertility-sparing treatment using progestin therapy is known to be safe and effective. International recommendations advise the use of megestrol acetate or medroxyprogesterone acetate. However, chlormadinone acetate has fewer adverse effects and can be used in patients at high vascular risk. In the present prospective study, we aimed to confirm that the efficiency of 6 months chlormadinone acetate administration to obtain remission of atypical hyperplasia or stage 1A endometrial carcinoma is comparable to that of the use of other fertility-sparing treatments. Design A prospective, observational study. Setting Nationwide France PREFERE prospective registry. Population Women with endometrial hyperplasia or stage 1A cancer willing to preserve their fertility Methods All patients received three or six months of chlormadinone acetate and were evaluated by hysteroscopic resection and pipelle sampling every three months. Main outcome measure Complete remission rate. Results Ninety-four patients were included. Seventy-nine patients achieved complete remission at 6 months (84%). No patients stopped treatment due to a lack of tolerance. Twenty-four percent of the patients achieved a live birth during a twenty-eight months follow up. Conclusion Chlormadinone acetate is an effective and well-tolerated fertility-sparing treatment. Its benefits over other progestins is its tolerability, and its absence of contraindications which makes chlormadinone acetate a good choice for patients with thromboembolism and high vascular risk.