OBJECTIVE Levonorgestrel (LNG), delivered locally into the uterine cavity has a profound effect on the endometrium. The aim of the study was to use a LNG intrauterine system to treat non-atypical and atypical endometrial hyperplasia in women and to evaluate the long-term cure (remission) rate. METHODS Each of the 20 women in the study, of whom eight were diagnosed with atypical hyperplasia, received a LNG-IUS, releasing 20 microg LNG/day. The study is a non-comparative study with long-term follow-up (range 14-90 months). RESULTS All women developed a normal endometrium, except one asymptomatic woman with atypical hyperplasia who still had focal residual non-atypical hyperplasia at 3 years follow-up in the presence of a thin (< 4 mm) endometrium. CONCLUSIONS Continuous intrauterine delivery of LNG appears to be a promising alternative to hysterectomy for the treatment of endometrial hyperplasia and could enhance the success rate when compared with other routes of progestagen administration as well as intrauterine progesterone delivery. The significant reduction of the PR expression observed during treatment with the LNG-IUS appears to be a marker for the strong antiproliferative effect of the hormone at a cellular level resulting in an inhibition of estrogen bioactivity and endometrial suppression.