PURPOSE: This study aimed to determine whether administering intravesical chemotherapy (IVC) during the Bacillus Calmette - Guérin (BCG) waiting period after the second TURBT improves the recurrence-free survival (RFS) of patients with non - muscle - invasive bladder cancer (NMIBC). METHODS: A retrospective analysis was performed on patients who had undergone a second TURBT and subsequent intravesical BCG immunotherapy (IBI) at the Affiliated Hospital of Xuzhou Medical University between January 2012 and December 2023. The patients were divided into two groups (A and B) based on whether they continued IVC during the BCG waiting period, and RFS was compared between the two groups. RESULTS: A total of 164 patients were included in this study. The log-rank test results indicated that IVC administered during the BCG waiting period was associated with a more favorable RFS for patients with NMIBC, particularly those at high risk. Multivariate analysis revealed that pathological T-stage (HR 2.084, 95% CI [1.132, 3.834], p = 0.018) and IVC received during the BCG waiting period (HR 0.261, 95% CI [0.140, 0.488], p <
0.001) were significantly correlated with patient RFS. CONCLUSIONS: Administering IVC during the BCG waiting period is recommended to prolong the time to recurrence in patients with high-risk NMIBC. Conversely, this additional treatment is unnecessary for patients at intermediate risk.