Laparoscopic surgery is often carried out in women with endometriosis who experience dysmenorrhea. The results are not consistently good, and affected women often have recurrent pain. This open-label, parallel-group, randomized trial evaluated an intrauterine device (IUD) that releases levonorgestrel (a Lng-IUD), a potent 19-nortestosterone derivative progestin that can induce amenorrhea. Twenty parous women with endometriosis and moderate or severe dysmenorrhea received the Lng-IUD after operative laparoscopy, whereas 20 others had only surgery. The participants, who were 40 years of age or younger and did not want a child, were reevaluated after 12 months. Conservative surgery was performed using only mechanical instruments and electrosurgery. Adhesions were sectioned, the ovaries were mobilized, and areas of endometriosis were either excised or coagulated. The Lng-IUD that was inserted into the uterine cavity releases 20μg of levonorgestrel daily over 5 years. In one case, the Lng-IUD was displaced. After 12 months, amenorrhea was described by 28% of women given the Lng-IUD and dysmenorrhea or spotting by another 50%; 22% of these women had normal menstrual flow. Dysmenorrhea continued at a moderate or severe level in 45% of women treated by surgery alone. The absolute risk reduction of recurrent dysmenorrhea in the Lng-IUD group was 35%. Dyspareunia and nonmenstrual pain also were less frequent in the IUD group. Tolerable side effects developed in 8 of 20 women assigned to receive the IUD. At follow-up, 75% of women in the Lng-IUD group and 50% of those in the surgery-only group were satisfied or very satisfied with their treatment. This pilot study suggests that, in women with symptomatic endometriosis, inserting a Lng-IUD after conservative laparoscopic surgery reduces the chance of recurrent dysmenorrhea and provides a high level of patient satisfaction, at least over the medium term.