The objective of this study was to assess the efficacy and safety of a new transurethral microwave thermotherapy device, T3, in the treatment of symptomatic benign prostatic hyperplasia. A total of 155 patients were recruited at 3 sites and treated using an identical protocol. The mean AUA symptom score decreased by 58% at 12 months, by 61% at 24 months and by 56% at 36 months. The increase in mean peak flow rates at these time points was 3.9 (47%), 3.4 (44%) and 5.1 ml/s (67%), respectively. Adverse events were minor and the patients' satisfaction with treatment was high. Transurethral microwave thermotherapy with the T3 device provides a safe, effective treatment for symptomatic benign prostatic hyperplasia.