Hormonal agents have been used to treat endometrial cancer since the early 1960s. The response rate for patients with advanced or recurrent endometrial cancer subjected to gestagen therapy has been reported to be about 30%. However, the analysis of the action mechanism of gestagen on endometrial cancer is not complete. Since oral administration of high dose MPA has begun, thrombosis has been reported as an uncommon but severe side effect. The risk factors for thrombosis in patients having gestagen therapy were clarified in the report published by the Ministry of Welfare in 1992. This report emphasized the importance of patient selection for gestagen therapy and cautious management. Besides gestagen therapy, antiestrogen therapy has been tried for the treatment of endometrial cancer. However, tamoxifen therapy was not so effective compared with gestagen. Moreover, antiestrogen-gestagen combination therapy and chemo-endocrine therapy are on trial recently. These trials are attempts to find a more effective regimen for the treatment of endometrial cancer. A recent theme in the study of hormonal therapy is basic investigation concerning the effect of MPA upon the action of growth factor and oncogene expression in endometrial cancer cells. These studies may lead to a molecular biological explanation of the action mechanism of gestagen therapy in future.