Long-term comparative effectiveness research of localized prostate cancer treatments is scarce, evidence lacking specially for brachytherapy. The aim of this study was to assess the long-term impact of the side effects of radical prostatectomy, brachytherapy, and external radiotherapy on patients with localized prostate cancer at 10 years, using propensity score analyses. This was a prospective observational study of a cohort of men diagnosed with clinically localized prostate cancer (clinical stage T1 or T2, low and intermediate risk group), and treated with: radical prostatectomy (n=192), brachytherapy (n= 317) or external radiotherapy (n=195). Treatment election was jointly made by patients and physicians. Patient-Reported Outcomes (PRO) evaluation included the Expanded Prostate Cancer Index Composite (EPIC) and the Short Form-36, administered centrally by telephone interviews before and annually after treatment. EPIC covers urinary, bowel, sexual, and hormonal domains. To assess PRO changes over time, while accounting for correlation among repeated measures, generalized Estimating Equation (GEE) models adjusted by propensity score were constructed. PROs completion rate at 10 years was 85.8%. GEE models showed that the pattern of radical prostatectomy's side effects, with large urinary incontinence and sexual dysfunction, remained until ten years after treatment: -1.1 and -1.3 standard deviations (SD). Brachytherapy produced late deterioration on urinary continence (-0.4 SD) and sexual function (-0.9 SD) that appeared at mid-term, but differences from radical prostatectomy remained statistically significant at 10 years (p