In Japan, Duphaston® Tablets have appeared in 1965 for the treatment of endometriosis and been used at some medical institutions. However, after releasing of danazol in the early 1980's and gonadotropin-releasing hormone (GnRH) agonists in the late 1980's, pseudomenopause therapy became mainstream because of its high efficacy. However, pseudopregnancy therapy was recognized again due to adverse reactions associated with pseudomenopause therapy. After 2000, low-dose estrogen/progestin (LEP) combination drugs (as LEP products, ethinylestradiol/norethisterone combination drug and ethinylestradiol/drospirenone combination drug) and dienogest have been utilized as drugs that are safer and can be administered for a long time. In recent years, Duphaston® Tablets are increasing recognized again from the viewpoints of its efficacy and safety because the drug has no effect to inhibit ovulation or effect on basal body temperature, a diagnosis of ovulation and other conditions may be made by following up basal body temperature, and pregnancy may be achieved even during treatment with Duphaston. As previously mentioned, Duphaston® Tablets are an old drug, and there are only few clinical data from Japanese patients; thus, its latest clinical efficacy and safety data are being demanded again mainly by obstetrician-gynecologists.