The safety and effectiveness of tissue ablation by coagulative necrosis with high-intensity focused ultrasound (HIFU) applied through a rectal probe to 36 patients with symptomatic benign prostatic hyperplasia (BPH) was investigated in a phase II clinical trial. Overall, HIFU treatment was well tolerated, the mean hospital stay being 1.1 days. Negative side effects were transient urinary retention in 32/36 patients, hematuria in 2 patients and hematospermia resolving after 3-4 weeks (n = 15). After 3 months the maximum flow rate/s (Qmax) increased from 9.0 +/- 3.9 to 14.4 +/- 7.0 ml/s, the median flow rate/s (QM90) from 4.9 +/- 2.4 to 7.6 +/- 4.17 ml/s; the postvoid residual volume decreased from 128 +/- 88 to 57 +/- 35 ml and the AUA symptom score from 25.5 +/- 5 to 13.2 +/- 4.4. In conclusion, it was shown that tissue ablation in patients with symptomatic BPH using HIFU is safe and dramatically reduces both obstructive and irritative symptoms and leads to a significant increase in uroflow and a decrease in postvoid residual volume.