To evaluate the influence of patient-associated parameters and comorbities, with a special focus on renal function after intravesical adjuvant bacillus Calmette-Gue´rin (BCG) immunotherapy in patients with non-muscle-invasive bladder cancer (NMIBC). We retrospectively reviewed the medical records of patients treated from October, 1991 to December, 2013 at Seoul National University who were diagnosed with NMIBC and treated with intravesical BCG. A total of 344 patients who were diagnosed with NMIBC and treated with intravesical BCG were enrolled in this study. Tumor recurrence was observed in 171 patients (49.3%); progression to higher pT category or grade was found in 68 patients (15.1%). Multivariate analysis demonstrated that recurrent tumors and the presence of multiple tumors increased the risk of recurrence. However, other factors also appeared to predict recurrence, such as impaired renal function (<60 ml/min), which was associated with recurrence in univariate and multivariate analyses (HR 1.879 p = 0.008). It is worthy of notice that impaired renal function was an independent predictor of tumor recurrence after BCG instillation in multivariate analysis. Therefore, we should consider not only the clinical or pathologic findings of a tumor but also renal function during decision-making for additional therapy.