PURPOSETo describe the biochemical failure-free survival (BFFS), GU toxicity and erectile dysfunction in intermediate risk prostate cancer treated with iodine 125 monotherapy (I125).PATIENTS AND METHODSBetween October 1994 and October 2007, 1282 patients were treated with I125 at the Hotel Dieu de Quebec. Two hundred patients were intermediate risk prostate cancer. One hundred and fifty-seven had enough follow-up to be evaluated in this study. Biochemical failure-free survival is reported using Phoenix definition. Acute and late GU toxicity was described using the International Prostate Symptoms Score (IPSS) as well as with the rate of bladder catheter. Erectile dysfunction was also reported.RESULTSThe mean age of the patients was 65.6 years (S.D.=6 years) and the mean pretreatment PSA was 8.7ng/ml. About half of the patients (51%) were T2b/T2c. About 44.6% had a PSA greater than 10 and 4.5% had Gleason score of 7/10. More than half of the patients received a short course of hormones of less than 6 months for cytoreduction (57.4%). The median follow-up was 60 months. Biochemical failure-free survival at 60-month and 96-month were 87.1% and 81% according to Phoenix definition. The mean IPSS rose from 5 immediately after the implant to 15 1 month after and then slowly decreased to 8 at 24 months. Acute urinary retention with bladder catheter occurred in 10.9% of patients. Only 4.3% presented erectile dysfunction at 5 months post-implant.CONCLUSIONI125 monotherapy for intermediate risk prostate implant gives biochemical failure-free survivals at 5 years and 8 years comparable to those obtained with high dose external beam radiotherapy. GU toxicity and erectile dysfunction were low and acceptable. Therefore, the use of I125 alone in this group of patients could be presented and discussed with the patient in the waiting of phase III validation.