BackgroundThe aim of this study was to describe changes in patient-reported functional outcome measures (PROMs) comparing pre-treatment and 12 months after radical prostatectomy (RP), external beam radiation therapy (EBRT), brachytherapy and active surveillance (AS).MethodsMen enrolled from 2010 to 2019 in the South Australian Prostate Cancer Clinical Outcomes Collaborative registry a prospective clinical registry were studied. Urinary, bowel, and sexual functions were measured using Expanded Prostate Cancer Index Composite (EPIC-26) at baseline and 12 months post-treatment. Higher scores on the EPIC-26 indicate better function. Multivariable regression models were applied to compare differences in function and extent of bother by treatment.ResultsOf the 4926 eligible men, 57.0% underwent RP, 20.5% EBRT, 7.0% brachytherapy and 15.5% AS. While baseline urinary and bowel function varied little across treatment groups, sexual function differed greatly (adjusted mean scores: RP = 56.3, EBRT = 45.8, brachytherapy = 61.4, AS = 52.8; p < 0.001). Post-treatment urinary continence and sexual function declined in all treatment groups, with the greatest decline for sexual function after RP (adjusted mean score change − 28.9). After adjustment for baseline differences, post-treatment sexual function scores after EBRT (6.4; 95%CI, 0.9–12.0) and brachytherapy (17.4; 95%CI, 9.4–25.5) were higher than after RP. Likewise, urinary continence after EBRT (13.6; 95%CI, 9.0-18.2), brachytherapy (10.6; 95%CI, 3.9–17.3) and AS (10.6; 95%CI, 5.9–15.3) were higher than after RP. Conversely, EBRT was associated with lower bowel function (− 7.9; 95%CI, − 12.4 to − 3.5) than RP. EBRT and AS were associated with lower odds of sexual bother (OR 0.51; 95%CI, 0.29–0.89 and OR 0.60; 95%CI, 0.38–0.96, respectively), and EBRT with higher odds of bowel bother (OR 2.01; 95%CI, 1.23–3.29) compared with RP.ConclusionThe four common treatment approaches for prostate cancer were associated with different patterns of patient-reported functional outcomes, both pre- and 12 months post-treatment. However, after adjustment, RP was associated with a greater decline in urinary continence and sexual function than other treatments. This study underscores the importance of collecting baseline PROMs to interpret post-treatment functional outcomes.