['The aim of this study was to investigate the clinical significance of CD4(+) T cells in non-muscle-invasive bladder cancer (NMIBC) tissues in situ.', 'Immunohistochemistry was used to examine the distribution of CD4(+) T cells in 131 NMIBC tissues. Kaplan-Meier analysis and Cox proportional hazards regression models were applied to estimate overall survival (OS) and recurrence-free survival (RFS).', 'NMIBC patients were divided into two groups based on the median frequency of CD4(+) T cells (median, 1/×400 high resolution). On univariate analysis, CD4(+) T cell density was inversely associated with overall survival (P = 0.01). In those patients with high CD4(+) T density, 5-year OS rates was only 77%, compared with 86% in those with low density, respectively. Although CD4(+) T cell density showed no prognostic significance for RFS (P = 0.36), 5-year RFS rates of patients with high CD4(+) T density (58%) was lower than those of patients with low CD4(+) T density (65%, respectively). By multivariate analysis, tumor infiltrating CD4(+) T cell density emerged as an independent prognostic factor for OS (HR, 2.75; P = 0.004). In addition, no association was found between CD4(+) T cell density and any clinicopathological variables (P > 0.05).'] Does high CD4⁺ T cell density is associate with poor prognosis in patients with non-muscle-invasive bladder cancer?