Background: Bladder cancer ranks as the 10th most common cancer globally. The diagnosis of bladder tumors typically involves cystoscopy. Objective: This study aimed to evaluate the sensitivity and specificity of cystoscopy in detecting bladder tumors within a surveillance program following a bladder cancer diagnosis. Design, Setting, and Participants: This study utilized recordings of cystoscopies conducted at the Department of Urology, Zealand University Hospital, between July 2021 and November 2022. Clinical observations were cross-referenced with pathological results or follow-up cystoscopies. Clinically negative cystoscopies were further scrutinized for potential overlooked tumors. Outcome Measurements and Statistical Analysis: Sensitivity and specificity of cystoscopy were assessed through ROC curve analysis. Results and Limitations: A total of 565 cystoscopies were recorded, with 135 indicating clinical positivity. Among 181 cystoscopies with clinically negative results that underwent a follow-up cystoscopy, 17 patients (9.4%) were subsequently diagnosed with bladder cancer, with the lesions identified in the initial cystoscopy. The sensitivity and specificity of cystoscopy in these cases were 81% and 73%, respectively. Conclusion: This trial underscores the underdiagnosis and undertreatment of bladder tumors within the current surveillance program. Additionally, aggressive malignant lesions may be overlooked, heightening the risk of disease progression. Therefore, it is recommended that cystoscopies be complemented by other diagnostic methods to ensure accurate diagnosis and proper patient treatment. Patient Summary: This study involved 316 patients who underwent video-recorded cystoscopies and subsequent follow-up. Of these patients, 181 initially exhibited no clinical signs of bladder cancer. However, upon reviewing the recorded cystoscopy, bladder cancer was identified in 17 patients (9.4%).