Secondary amenorrhea in women with normal estrogen levels increases the risk of endometrial carcinoma. Cyclical dydrogesterone induces regular withdrawal bleeding and effectively protects the endometrium of postmenopausal women receiving estrogens. In order to assess the efficacy of dydrogesterone in inducing regular withdrawal bleeds in premenopausal women with secondary amenorrhea or oligomenorrhea and normal estrogen levels, a double-blind, randomized, placebo-controlled, multicenter study was conducted in 104 women using cyclical dydrogesterone as is used for estrogen replacement therapy. Treatment consisted of dydrogesterone (10 mg/day on days 1-14 followed by placebo on days 15-28 of each cycle) given for six cycles of 28 days. The control group received placebo throughout the six cycles. Bleeding was documented by the patient on diary cards. The number of women with withdrawal bleeding during the first cycle was twice as high in the dydrogesterone group as in the placebo group (65.4% vs. 30.8%; p = 0.0004). Superiority of dydrogesterone was also observed for regularity of bleeding over the six cycles (p < 0.0001), although endometrial thickness after six cycles did not differ between the groups. In conclusion, dydrogesterone is significantly superior to placebo in inducing withdrawal bleeding, and maintaining regular bleeding, in women with secondary amenorrhea and normal estrogen levels.