This report presents the outcome of prostate permanent brachytherapy (PPB). One hundred and seventy-two patients with clinically localized prostate cancer were treated with permanent brachytherapy using iodine-125 seeds (125-I) at Hiroshima University Hospital from July 2004 to June 2010. This study evaluated the efficacy of PPB in these patients. The median patient age was 69 years (range 53 to 82 years), the median prostate-specific antigen (PSA) value before biopsy was 6.75 ng/ml (range 3.5 to 47.9 ng/ml), and the median prostate volume was 23.1 ml (range 10.1 to 57 ml). The median follow-up was 37 months (range 1 to 72 months). The serum PSA levels decreased continuously after PPB throughout the entire follow-up period in 97% of patients without neoadjuvant hormonal therapy. No relapse occurred during the follow-up period in patients at low risk. Our 6-year experience suggests that PPB is effective for localized prostate cancer. Patients with prostate cancer that does not require combined external beam radiation therapy (EBRT) have the best chance of responding to treatment.