Use of the levonorgestrel-releasing intrauterine system (LNG IUS) is associated with a strong reduction in the number of days of bleeding and menstrual blood loss. This effect is based on the marked local action of the intrauterine release of levonorgestrel (LNG) on the endometrium. In suppressed endometrium the production of many highly active compounds ceases. On the other hand, LNG stimulates the synthesis of some regulatory proteins in the endometrium. Reduction of menstrual blood loss results in improvement of the body iron balance and in an increase in hemoglobin concentration. The LNG IUS has been used in the prevention and treatment of iron deficiency anemia. Many studies have demonstrated that the LNG IUS is effective in the treatment of menorrhagia. Reduction of excessive blood loss is seen as soon as the first menstruation after insertion, and at 1 year the reduction is more than 90%. The therapeutic effect is maintained for more than 5 years after first placement of the LNG IUS in the uterine cavity. Correct insertion is essential, and complications and side effects are rare; fertility is preserved, and invasive procedures such as endometrial ablation or hysterectomy and hospitalization are avoided. The third major indication for therapeutic use is in protection of the endometrium in estrogen replacement therapy during peri- and postmenopausal years. A fundal position of the system in the uterine cavity results in reduction of bleeding, and an increasing number of women have no bleeding at all during use of the IUS. Acceptance and continuation of use of the LNG IUS in hormone replacement therapy (HRT) have been high.