Objective: To observe the effects of levonorgestrel-releasing intrauterine system (LNG-IUS) in treatment of chronic pelvic pain associated with adenomyosis (AM) and in prevention of its recurrence. Methods: A prospective continuing study including 180 patients with chronic pelvic pain associated with AM who received insertion of LNG-IUS who were divided into three groups depending on the pain severity. The visual analog scale (VAS) was used for pain assessment before and during the treatment and transvaginal ultrasonic measurement of the uterine size, while various side effects, were observed and recorded. Results: After placement of LNG-IUS, scores of pain and ratio of severe pelvic pain decreased significantly compared with baselines (p < 0.01), the scores of VAS were 9.0 ± 0.8, 6.5 ± 2.8, 4.3 ± 1.8, 3.3 ± 2.2, 2.2 ± 2.1, 2.2 ± 1.8, 1.4 ± 1.6 and 1.3 ± 1.3 at 0, 3, 6 and 12 months, respectively. During 12 months after placement of LNG-IUS, scores of pain had improved significantly compared with preceding period (p < 0.01). We found no universal dependent factors predicting improvement of pain, which was neither relevant with simultaneous changes of menstruation patterns nor with adverse effects (p > 0.005). Conclusion: The obtained results allowed to confirm the possibility of using LNG-IUS in the treatment of pelvic pain syndrome associated with AM, particularly with mild and moderately severe pelvic pain syndrome. This is a cost effective, reversible and long-term treatment for women with pelvic pain associated with AM, which reduces the need for surgical interventions. © 2016 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.