Purpose Earlier studies evaluating the effect on quality of life (QoL) of localized prostate cancer interventions included patients receiving adjuvant hormone therapy, which could have affected their outcomes. Our objective was to compare the QoL impact of the three most common primary treatments on patients who were not receiving adjuvant hormonal treatment. PATIENTS AND METHODS: This was a prospective study of 435 patients treated with radical prostatectomy, external-beam radiotherapy, or brachytherapy. QoL was assessed before and after treatment with the Short Form-36 and the Expanded Prostate Cancer Index Composite. Differences between groups were tested by analysis of variance. Distribution of outcome at 3 years was examined by stratifying according to baseline status. Generalized estimating equation models were constructed to assess the effect of treatment over time. RESULTS: Compared with the brachytherapy group, the prostatectomy group showed greater deterioration on urinary incontinence and sexual scores but better urinary irritative-obstructive results (-18.22, -13.19, and +6.38, respectively, at 3 years; P < .001). In patients with urinary irritative-obstructive symptoms at baseline, improvement was observed in 64% of those treated with nerve-sparing radical prostatectomy. Higher bowel worsening (-2.87, P = .04) was observed in the external radiotherapy group, with 20% of patients reporting bowel symptoms. CONCLUSION: Radical prostatectomy caused urinary incontinence and sexual dysfunction but improved pre-existing urinary irritative-obstructive symptoms. External radiotherapy and brachytherapy caused urinary irritative-obstructive adverse effects and some sexual dysfunction. External radiotherapy also caused bowel adverse effects. Relevant differences between treatment groups persisted for up to 3 years of follow-up, although the difference in sexual adverse effects between brachytherapy and prostatectomy tended to decline over long-term follow-up. These results provide valuable information for clinical decision making.