Background: Radical prostatectomy (RP) and brachytherapy (BT) are widely utilized treatments for favorable-risk prostate cancer (PC). We estimated the risk of PC-specific mortality (PCSM) following RP or BT in men with low- or intermediate-risk PC using prospectively collected data. Methods: The study cohort comprised 5,760 men with low-risk PC (prostate-specific antigen [PSA] level ≤ 10 ng/mL, clinical category T1c or 2a, and Gleason score ≤ 6), and 3,079 men with intermediate-risk PC (PSA level 10-20 ng/mL, clinical T2b or T2c, or Gleason score 7). Competing risks multivariable regression was performed to assess risk of PCSM after RP or BT, adjusting for age, treatment year, cardiovascular comorbidity, and known PC prognostic factors. Results: There was no significant difference in the risk of PCSM among men with low-risk PC (11 vs. 6 deaths: adjusted hazard ratio [AHR], 1.62; 95% CI, 0.59-4.45; P = 0.35) who received BT compared to RP. However among men with intermediate-risk PC, despite significantly shorter median follow-up for men undergoing BT as compared to RP (4.1 vs. 7.2 years, P < 0.001), there was a trend toward an increased risk of PCSM (18 vs. 9 deaths: AHR, 2.30; 95% CI, 0.95-5.58; P = 0.07) for men treated with BT. Conclusions: The risk of PCSM among men with low-risk PC was not significantly different following RP or BT, however there may be a reduced risk of PCSM after RP as compared to BT in men with intermediate-risk PC.