Clinical trials have consistently shown that the IUD that releases 20 micrograms levonorgestrel daily (LNG-IUD-20) has a contraceptive efficacy comparable to, if not surpassing, the Copper T380 and the Multiload Copper-375 IUDs. The focus of this review is the device's non-contraceptive effects--the beneficial ones, such as reduction of menorrhagia, a therapeutic effect on dysmenorrhea, and prevention of ectopic pregnancy, as well as the deleterious ones, such as amenorrhea, spotting and irregular bleeding, hormonal side-effects, and functional ovarian cysts. Also discussed are the possibility of a preventive effect on pelvic inflammatory disease, the effects of the IUD on postpartum/lactating women, fertility return after removal and other safety issues. In general, the LNG-IUD-20's non-contraceptive benefits are substantive, carry important medical and public health implications, and far outweigh the device's deleterious effects, which are either medically mild or transient in nature, and can usually be managed satisfactorily by counseling. A better understanding of these effects, both beneficial and deleterious, of this hormone-releasing IUD should lead to more effective patient counseling, which, in turn, should improve user quality of life, minimize unnecessary removals, and maximize continuation of use.