Background: Immunotherapy improves overall survival (OS) in the second and later lines of renal cell car-cinoma (RCC) treatment. Recent studies have suggested that antibiotic (ATB) use either shortly before or after the start of immunotherapy could lead to decreased OS. Herein, we evaluate the impact of ATB use on OS in RCC patients treated with nivolumab in a multi-center cohort from Turkey. Methods: The data of 93 metastatic RCC patients treated with nivolumab in the second line or later were retrospectively collected from 6 oncology centers. Previous treatments, sites of metastases, International Metastatic RCC Database Consortium risk classification, and ATB use in the three months before (-3) or three months after ( + 3) the start of immunotherapy were recorded together with survival data. The as- sociation of clinical factors with OS and progression-free survival (PFS) was analyzed with univariate and multivariable analyses. Results: The median age was 61 (interquartile range 54-67), and 76.3% of the patients were male. The median OS of the cohort was 23.75 +/- 4.41, and the PFS was 8.44 +/- 1.61 months. Thirty-one (33.3%) patients used ATBs in the 3 months before (-3) or 3 months after ( + 3) nivolumab initiation. In the multivariable analyses, ATB exposure (HR: 2.306, 95% confidence interval [CI]: 1.155-4.601, P = 0.018) and the presence of brain metastases at the baseline (HR: 2.608, 95% CI: 1.200-5.666, P = 0.015) had a statistically significant association with OS, while ATB exposure was the only statistically significant parameter associated with PFS (HR: 2.238, 95% CI: 1.284-3.90 0, P = 0.004). Conclusion: In our study, patients with ATB exposure in the 3 months before or 3 months after the start of immunotherapy had shorter OS. Our findings further support meticulous risk-benefit assessments of prescribing ATBs for patients who are either receiving or are expected to receive immunotherapy. (c) 2021 Elsevier Inc. All rights reserved.