Objective: To evaluate the use of a levonorgestrel-releasing intrauterine system (LNG-IUS) for treating endometrial hyperplasia in patients with polycystic ovary syndrome (PCOS). Methods: LNG-IUSs were inserted in 60 PCOS patients with simple (40 cases), irregular (12 cases), or complex (8 cases) endometrial hyperplasia. Follow-ups were performed at 3, 6, 12, and 24 months after insertion. At each time point, changes in menstruation, hemoglobin level, and endometrial thickness and pathology were recorded. Menstrual changes were assessed with the Pictorial Blood Assessment Chart. Hemoglobin levels were measured by the Blood Routine Test. Endometrial thickness was determined by transvaginal ultrasound. Endometrial pathology was defined as simple, irregular, or complex endometrial hyperplasia by a pathologist after curettage. Outcomes at each time point were compared to baseline (pre-insertion) measurements by Student's t test or ANOVA (for multiple comparisons) with the post hoc Dunnett's test. Differences with a p < 0.05 were considered statistically significant. Results: At all time points after LNG-IUS insertion and in all patients, menstrual blood loss was decreased and hemoglobin level was increased significantly compared to pre-insertion levels. The endometrial thickness was significantly reduced in all groups after 12 months. Most patients showed transformation of the endometrial pathology, with complete disappearance of simple and irregular cases of endometrial hyperplasia and a decreased number of complex endometrial hyperplasia cases. Conclusions: LNG-IUS is an effective, safe, nonsurgical, and atraumatic approach with few side effects for the treatment of endometrial hyperplasia in patients with PCOS.