Canine and human histological studies have proved the safety and efficacy of contact-free intraprostatic tissue ablation by transrectal high-intensity focused ultrasound. Data from an international phase II clinical trial for benign prostatic hyperplasia have demonstrated an improvement of symptoms, uroflow, residual volume, and urodynamic parameters. Histological data and clinical results from a pilot study look promising for treating localized prostate cancer in the future. At present, the high-intensity focused ultrasound procedure is modified with respect to transducer design, duty cycle, and treatment protocol to enhance the clinical efficacy.