To assess the impact of confirmatory tests on active surveillance (AS) biopsy disease reclassification and progression to treatment in men with favorable risk prostate cancer (FRPC). We searched the MUSIC registry for men with FRPC managed with AS without or with a confirmatory test. Confirmatory tests included (1) repeat prostate biopsy, (2) genomic tests, (3) prostate magnetic resonance imaging (MRI), or (4) MRI followed by a post-MRI biopsy. Confirmatory test results were deemed reassuring (RA) or nonreassuring (nonRA) according to predefined criteria. Kaplan-Meier curves and multivariable Cox regression models were used to compare surveillance biopsy disease reclassification-free survival and treatment-free survival. Of the 2,514 men with FRPC who were managed on AS, 1211 (48%) men obtained a confirmatory test. We noted differences in the 12-month unadjusted surveillance biopsy disease reclassification-free probability (68%, 83%, and 90%, P < .0001) and 24-month unadjusted treatment-free probability (55%, 81%, and 79%, P < .0001), for men with nonRA confirmatory tests, no confirmatory test, and RA confirmatory tests, respectively. Excluding patients with genomic confirmatory tests, men with RA confirmatory tests were associated with a lower hazard (hazard ratio HR 0.57, 95% confidence interval CI 0.38-0.84, P = .005) and men with nonRA confirmatory tests had an increased hazard (HR 1.97, 95% CI 1.22-3.19, P = .006) of surveillance disease reclassification compared with men without confirmatory tests in the multivariable model. These data suggest men with RA confirmatory tests have less surveillance biopsy reclassification and remain on AS longer than men with nonRA test results. Confirmatory tests may help risk stratify men considering active surveillance.