Study Objective: To prospectively evaluate the clinical effectiveness and safety of ultrasound-guided percutaneous microwave ablation for symptomatic subserosal uterine myomas. Design: Prospective observational study (Canadian Task Force classification II-1). Setting: A teaching hospital (Department of Interventional Ultrasound, General Hospital of Chinese PLA, Beijing, China). Patients: Sixty-nine patients with symptomatic subserosal uterine myomas treated with ultrasound-guided percutaneous microwave ablation. Interventions: All 69 patients underwent ultrasound-guided percutaneous microwave ablation. The number of patients lost to follow-up at was 21 at 3 months, 34 at 6 months, and 35 at 12 months. Measurements and Main Results: The efficacy of treatment was evaluated based the mean myoma volume shrinkage rate and changes in Uterine Fibroid Symptom and Quality of Life Questionnaire scores at 3, 6, and 12 months after therapy. Treatment safety was evaluated based on the Society of Interventional Radiology practice guidelines. The mean patient age was 40.3 +/- 4.9 years (range, 26-49 years). The mean myoma volume was 221.74 +/- 153.18 cm(3) before ablation, decreasing to 87.24 +/- 45.93 cm 3 at 3 months after ablation (p < .001), 46.68 +/- 24.7 cm(3) at 6 months after ablation (p < .001), and 38.05 +/- 24.93 cm(3) at 12 months after ablation (p <.001), respectively. Between pretreatment and 3-month follow-up, the mean symptom severity score decreased from 34.53 +/- 3.83 to 12.74 +/- 3.07 (p < .001), and the mean health-related quality of life score increased from 45.25 +/- 10.97 to 78.48 +/- 11.39 (p < .001). Both scores remained stable at the 6- and 12-month follow-up time points. No permanent injury or fatal complications were seen in this series. Conclusion: Ultrasound-guided percutaneous microwave ablation of subserosal uterine myomas is a promising treatment method. Further studies with larger sample sizes and a control group are needed. (C) 2018 Published by Elsevier Inc. on behalf of AAGL.