We evaluated the efficacy and feasibility of high-intensity-focused ultrasound (HIFU) for localized prostate cancer. Seventy patients received HIFU using Sonablate® 500 (Focus Surgery, IN, USA). In patients whose cancer was confined to only one lobe by multi-regional biopsies, total peripheral zone and a half portion of transitional zone were ablated (focal therapy). Otherwise, patients received whole organ ablation (whole therapy). Scheduled biopsies were performed at 6 and 12 months after treatment. Pre- and post-HIFU serum testosterone levels were measured. The 2-year biochemical disease-free survival (DFS) rates in patients at low, intermediate and high risk were 85.9, 50.9 and 0%, respectively, (P = 0.0028). After 12 months, 81.6% (40/49) of patients were biopsy negative; 84.4% in patients who received whole therapy, whereas 76.5% in those with focal therapy. The 2-year biochemical DFS rates for the patients at low and intermediate risk was 90.9 and 49.9%, respectively, in patients with whole therapy, whereas 83.3 and 53.6% in patients with focal therapy. In patients without neoadjuvant androgen deprivation, serum testosterone levels continuously decreased after whole therapy, whereas no changes were seen in those with focal therapy. The patients whose follow-up biopsies were positive tended to have significantly higher changes in prostate-specific antigen levels than biopsy-negative patients. In patients with low-risk prostate cancer, HIFU monotherapy resulted in comparable immediate cancer control with other modalities. Particularly, focal therapy might offer a feasible minimally invasive therapeutic option, which maintained serum testosterone level. To our knowledge, this is the first report that whole, but not focal, therapy affects the serum testosterone level.