Endometrial hyperplasias, which occur in the premenopausal age and are often induced by anovulatory cycles, are kept under control by progestin therapy. The good results with natural and synthetic progestins suggest that this treatment can be used both in premenopause and postmenopause hyperplasia. The progestin effect on the endometrium appears through a marked pseudodecidual reaction of the stroma and functional atrophy of the glands. These events are reported in the literature as inactive or suppressed endometrium and there is no physiological equivalent.