Aim: We retrospectively evaluated the role of neutrophil-to-lymphocyte ratio (NLR) and lymphocyte-to-monocyte ratio (LMR) as prognostic factors in metastatic non-small-cell lung cancer patients treated with nivolumab. Materials & methods: Medical records of 65 patients were reviewed. NLR and LMR were calculated at baseline (t0) and at first radiological tumor assessment (t1). Results: At univariate analysis, low NLR or high LMR values at t0 were associated with longer overall survival (p = 0.0001). At multivariate analysis including NLR and LMR at t0 and t1 and their trend, only NLR at t1 (p < 0.0001) and NLR trend (p < 0.0001) were significantly associated with overall survival outcomes. Conclusion: Our study suggests that NLR value at first tumor assessment or NLR trend could be used as prognostic indicators during nivolumab treatment in metastatic non-small-cell lung cancer.