The aim of this retrospective study was to evaluate the efficacy of levonorgestrel intrauterine system-releasing (LNG-IUS) insertion in preventing atypical endometrial hyperplasia (AH) and endometrial cancer (EC) in symptomatic postmenopausal overweight/obese women. A total of 34 overweight/obese postmenopausal women, presenting abnormal uterine bleeding (AUB) and endometrial hyperplasia (EH), and who were submitted to LNG-IUS insertion, were identified from registry data. Endometrial histology at LNG-IUS insertion showed simple EH in 20 cases (58.8%), complex EH in 14 cases (41.2%). At 36 months, 91% of patients showed no recurrence of AUB and a significant reduction in the mean endometrial thickness (from 8.2 ± 2.2 to 3.2 ± 1.5 mm, p < 0.05) was observed. Histologic regression of EH was observed in 27 (79.4%) and 33 (97.5%) cases at 12 and 36 months, respectively. None of the women in which EH persisted, reported cellular atypia or cancer progression at 12 and 36 months of follow-up. LNG-IUS represents an effective treatment option to manage postmenopausal obese women affected by AUB and EH. The device seems to be able to prevent the onset of AH and EC in women at high risk. Further prospective controlled studies in a well selected group of women are needed.