BACKGROUND Transrectal high-intensity focused ultrasound (HIFU) is under investigation as a minimally invasive therapeutic option for elderly men with prostatic cancer. METHODS From November 1996 to April 1999, 315 HIFU treatments with the Ablatherm (EDAP/TMS) were performed. A questionnaire including 50 theoretically possible adverse events was developed. Every patient complaint was recorded, including the physician's and patient's assessment, before and after therapy. Start date, end date, and period of every complaint were analyzed. RESULTS As major adverse events after primary HIFU, there were six cases of stress incontinence grade 1. After repeat treatments with HIFU, rectourethral fistulas occurred in five patients, stress incontinence grade 1 in eight, and, after additive transurethral resection, grade 2 in one and grade 3 in two patients. Post-HIFU rectal mucosa burn decreased from 15% in 1996 to 0 within the last year. In all treatments, obstruction was avoided by suprapubic urinary diversion. Urinary tract infections (UTIs) were recorded initially in 58% of patients but later in only 8%. CONCLUSIONS Transrectal HIFU proved to be a secure, minimally invasive therapeutic option for elderly men to avoid hormonal ablation or to postpone its first use.