We evaluated the efficacy, safety and impact on quality of life of a newly designed microwave thermal ablation system in patients with benign prostatic hyperplasia (BPH). Microwave thermal ablation was administered to 154 BPH patients at 3 centers in Canada and the United Kingdom during a single 1 to 2-hour office or clinic procedure without general or regional anesthesia and without need for potent medications necessitating intensive patient monitoring. Various measures of symptoms, voiding function and patient quality of life were assessed at baseline, 6 weeks, and 3, 6, 9 and 12 months after treatment. Mean American Urological Association symptom score 12 months after treatment (8.8, 95% confidence interval 7.7 to 10.0) was significantly lower (p <0.05) by 56% than that at baseline (20.1, 95% confidence interval 19.1 to 21.0). The incidence of mild symptoms increased from 0 to 57%, while that of severe symptoms decreased from 49 to 8%. There was a significant increase (p <0.05) in peak flow rate of 45% from 9.3 ml. per second (95% confidence interval 8.8 to 9.7) at baseline to 13.4 ml. per second (95% confidence interval 12.5 to 14.4) at 12 months. Similar symptomatic and urodynamic improvements occurred in all prostate volume categories. Convalescence was rapid after treatment with little or no need for home bed rest or restriction of usual activities. Patients expressed a high level of satisfaction with treatment and found the prostate symptoms to be significantly more tolerable. Adverse events were infrequent, transient and readily managed. Microwave thermal ablation proved to be safe and effective for treatment of BPH with a significant positive impact on patient quality of life.