Introduction: In order to optimize clinical and therapeutic approaches for patients with brain metastasis (BM), prognostic markers need to be widely available and simple to execute. Objective: Considering that a Complete-Blood-Count is usually obtained at the initial routine work-up of almost all oncologic patients, the aim of this study was to determine the utility of the neutrophil-to-lymphocyte-ratio (NLR) and the platelet-to-lymphocyte-ratio (PLR) as prognostic markers for BM. Results: A total of 550 patients with systemic cancer were included. Median age at the time of cancer diagnosis was 49 years and median age at the time of BM was 51 years. Median followup time was 11.2 months. Employing NLR cutoff values at BM diagnosis, patients were divided into groups I to III (I: <3, II: 3-4.49, III: >4.5), and median overall survival (MOS) was calculated for each one (I: 20 months, II: 13.9 months, and III: 7.5 months). Groups divided by a PLR cutoff (I: 250, II: ≥250) also differed in MOS (13.9 vs. 9.3 months). After multivariable analysis, only NLR was a significant independent predictor of MOS [I vs. II: 1.5 Odds Ratio (OR); I vs. III: 1.9 OR], meaning that NLR obtained at the time of BM diagnosis was inversely associated with MOS. Conclusion: The NLR, but not the PLR, is predictive of outcome in cancer patients with BM, therefore, NLR might serve as a complement to the already known prognostic scales.