OBJECTIVE: To compare the efficacy of the levonorgestrel-releasing intrauterine system (LNG-IUS) and oral norethisterone acetate (NET) for treatment of non-atypical endometrial hyperplasia in perimenopausal women. METHODS: One hundred and twenty perimenopausal women with non-atypical endometrial hyperplasia were selected in this randomized controlled trial. Patients received LNG-IUS (n=59) or NET (n=61; 15 mg/day for 3 weeks/cycle) for 3-6 months. Outpatient follow-up with endometrial biopsies were undertaken at 3, 6, and 12 months intervals after treatment. Outcome measures were; the regression rate, the time to regression and hysterectomy rate. RESULTS: A significantly higher regression rate was noted in the LNG-IUS group than in NET group at the 3rd, 6th and 12th month follow-up visits using intention-to-treat analysis (67.8% vs. 47.5%, relative risk [RR], 1.42; 79.7% vs. 60.7%, RR, 1.31; and 88.1% vs. 55.7%, RR, 1.58, respectively). However, no significant difference was found regarding the median time to regression (3 months). The hysterectomy rate during the follow-up period was significantly higher in the NET group (57.4% vs.22%, p<0.001). CONCLUSION: LNG-IUS treatment of non-atypical endometrial hyperplasia in perimenopausal women is more effective than NET for achieving disease regression for the majority within 1 year. Moreover, it can reduce the number of hysterectomies performed.