OBJECTIVE: Endometrial hyperplasia, an entity considered a precursor to endometrial carcinoma, frequently develops in women receiving unopposed estrogens. Progestins used concomitantly with estrogens can largely prevent endometrial hyperplasia and carcinoma. However, the ability of progestins to reverse endometrial hyperplasia induced by estrogens is less well recognized. The purpose of this study was to assess the medical reversal rate of endometrial hyperplasia that develops in women receiving unopposed estrogen replacement therapy (ERT). DESIGN: Review of recent literature (1990-2000). RESULTS: Based on four large series, more than 90% of endometrial hyperplasia caused by ERT can be reversed by medical treatment. Discontinuation of estrogen and oral administration of 10 mg/day of medroxyprogesterone acetate continuously for 6 weeks or cyclically for 3 months (2 weeks of each month) are the two regimens most widely used. Other progestins also have been shown to be effective. CONCLUSIONS: Progestins are highly successful in reversing endometrial hyperplasia caused by ERT.