Objectives: To assess the rate and predictive factors of urinary retention after iodine 125 brachytherapy for localized prostate cancer. Methods: Between 1998 and 2006, 655 patients with localized prostate cancer (T1-2, Gleason score 7 or less) were treated with brachytherapy at our institution. 42% received neoadjuvant hormonotherapy for prostate downsizing or when brachytherapy was combined with external beam radiation (10%). They underwent real-time interactive implantation (79%) or a preplanned technique (21%). Clinical, treatment-related and dosimetric factors were evaluated for catheterization requirement because of urinary retention. All patients received α1-blockers before and throughout at least 30 days posttreatment. Results: Twenty-one (3.2%) patients required catheterization because of urinary retention. Median time to retention onset was 1 day postimplantation. Univariate and multivariate analyses demonstrated that preimplant ultrasound (US)-based prostate volume and preimplant international prostate symptom scores (IPSS) were significant independent predictive factors for urinary retention (odds ratio [OR] = 6.8 and 3.1, 95% CI = 2.3-11.4 and 0.2-5.9, P = 0.02 and P = 0.03, respectively). Eight catheterized patients were successfully relieved from their catheter by nonsurgical means and 13 underwent minimal (channeling) transurethral resection of the prostate (TUR-P) not earlier than 6 months postimplant. Mean volume of resected prostate tissue was 9.9 mL (range 4.5-15). The perioperative and postoperative courses were uneventful. There was no TUR-P-related incontinence. Conclusions: Catheterization for acute urinary retention after brachytherapy is an uncommon event. Our data suggest that preimplant US-based prostate volume and IPSS are the strongest predictors for catheterization. Catheterized patients who are refractory to medical therapy can safely undergo a minimal TUR-P.