PURPOSE: Radical prostatectomy and brachytherapy are widely used treatments for favorable risk prostate cancer. We estimated the risk of prostate cancer specific mortality following radical prostatectomy or brachytherapy in men with low or intermediate risk prostate cancer using prospectively collected data. MATERIALS AND METHODS: The study cohort comprised 5,760 men with low risk prostate cancer (prostate specific antigen 10 ng/ml or less, clinical category T1c or 2a and Gleason score 6 or less), and 3,079 with intermediate risk prostate cancer (prostate specific antigen 10 to 20 ng/ml, clinical category T2b or T2c, or Gleason score 7). Competing risks multivariable regression was performed to assess the risk of prostate cancer specific mortality after radical prostatectomy or brachytherapy, adjusting for age, year of treatment, cardiovascular comorbidity and known prostate cancer prognostic factors. RESULTS: After a median followup of 4.2 years (IQR 2.0-7.4) for low risk and 4.8 years (IQR 2.2-8.1) for intermediate risk men, there was no significant difference in the risk of prostate cancer specific mortality among low risk (adjusted hazard ratio 1.62, 95% CI 0.59-4.45, p = 0.35) or intermediate risk men (AHR 2.30, 95% CI 0.95-5.58, p = 0.07) treated with brachytherapy compared with radical prostatectomy. The only factor associated with an increased risk of prostate cancer specific mortality (AHR 1.05, 95% CI 1.01-1.10, p = 0.03) was increasing age at treatment in intermediate risk men. CONCLUSIONS: The risk of prostate cancer specific mortality in men with low or intermediate risk prostate cancer was not significantly different following radical prostatectomy vs brachytherapy.