Recently, the number of cases of endometrial cancer has increased in Japan. Most of the increase are accounted for by premenopausal cases, which are frequently positive for ER or PR. Hormonal treatment using progestins such as MPA has been widely applied to endometrial cancer patients under 40 years old under the conditions of grade 1 well-differentiated endometrioid adenocarcinoma without myometrial invasion. In our hospital, we applied high-dose (600 mg/day) MPA for over 8 weeks in 14 cases of endometrial cancer, of which adenocarcinoma disappeared in 12 cases (86%), followed by cyclic administrations of low-dose MPA, with 7 subsequent recurrences. We think that a protocol for improving ovarian function, such as active induction of ovulation, should be established to induce intrinsic progesterone sufficient for the prevention of the recurrence of endometrial cancers. In the 2 cases, in which adenocarcinoma remained even after long administrations of MPA, myometrial invasion was noted in the surgically resected specimens. For advanced or recurrent endometrial cancers, MPA has been reported to be effective in an average of 26% in several reports, and effective in 42% cases when applied with combination chemotherapy, such as CAP, by virtue of the "chemical modulator" effect, which can delay the acquired resistance against ADM or CDDP. Furthermore, MPA has resulted in a significant improvement of 5-year disease-free survival rate when used as adjuvant therapy after complete operations and whole pelvic irradiation, compared with administrations of 5-FU in a randomized controlled study in Japan. Thus, in the future, we consider that hormonal therapy will play a more important role in endometrial cancer treatment.