Background: The surveillance of non-muscle invasive bladder cancer (NMIBC) requires frequent cystoscopies, which are costly and uncomfortable for patients. Uromonitor is a validated non-invasive urinary test for detecting NMIBC recurrence. However, data on its clinical benefit in an NMIBC surveillance program is limited. Objective: To assess the diagnostic accuracy of Uromonitor in NMIBC surveillance and its potential to limit the number of cystoscopies. Design, Setting, and Participants: The study included 202 patients with previous low-grade (LG) NMIBC tumors. Newly diagnosed patients were scheduled for flexible cystoscopy and Uromonitor test at 4, 12, and 24 months from the time of diagnosis. Patients with tumors diagnosed before entering the study underwent cystoscopy and Uromonitor test at the start of the study and 12 and 24 months from inclusion in the study. Outcome Measurements and Statistical Analysis: Sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV). Results and Limitations: Between February 2020 and October 2022, 202 patients were enrolled in the study. Of these patients, 171 met the eligibility criteria to perform the analysis, with a median age of 69 years, IQR (62–74), and 380 flexible cystoscopies with simultaneous Uromonitor tests. Overall, 39/171 (22.8%) patients had recurrences. Uromonitor showed a sensitivity of 89.7%, specificity of 96.2%, PPV of 72.9%, and NPV of 98.8%. In 28 cases, flexible cystoscopy was falsely positive, leading to surgery, where Uromonitor showed negative results. There were 13 cases of possible false positives for Uromonitor where flexible cystoscopy was negative. Conclusions: Uromonitor displays high diagnostic accuracy in detecting NMIBC recurrence with the potential for reducing the number of flexible cystoscopies in the follow-up of low- and intermediate-risk NMIBC. Patient Summary: We followed up on newly and previously diagnosed patients with LG NMIBC. We concluded that Uromonitor could potentially reduce the number of cystoscopies in NMIBC surveillance programs.