Background: The white blood cell count is one of the most sensitive markers associated with inflammation. The neutrophil/lymphocyte count ratio may be an independent factor for breast cancer mortality. Aim: To assess the predictive value of the neutrophil/lymphocyte ratio for mortality in breast cancer. Material and methods: Review of the database of a cancer center of a University hospital. Patients with infiltrating breast cancer treated between 1997 and 2012 were selected. The pathology type and lymph node involvement were obtained from the pathology report. The expression of estrogen, progesterone and Human Epidermal Growth Factor Receptor 2 (HER2) was determined by immunohistochemistry or in situ fluorescent hybridization (FISH). The absolute peripheral neutrophil and lymphocyte counts were obtained from a complete blood count obtained at least three months before treatment. Patients were followed for a median of 61 months (range 1-171). Results: From 323 eligible patients, after excluding those in stage IV and those without an available complete blood count, 131 patients were analyzed (81 with negative receptors and 117 HER2 enriched). The neutrophil/lymphocyte ratio was similar in both type of tumors (2.1 and 1.91 respectively). Twenty two patients died during follow up. Surviving patients with HER2 enriched tumors had a lower neutrophil/lymphocyte ratio than those who died (1.79 and 3.21 respectively, p < 0.01). In a multivariate analysis, including age, tumor stage and lymph node involvement as confounding factors, the neutrophil/lymphocyte ratio was still significantly associated with a risk of death with a hazard ratio of 2.56. Conclusions: A high neutrophil/lymphocyte ratio in the complete blood count can be a predictor of death in breast cancer.Background: The white blood cell count is one of the most sensitive markers associated with inflammation. The neutrophil/lymphocyte count ratio may be an independent factor for breast cancer mortality. Aim: To assess the predictive value of the neutrophil/lymphocyte ratio for mortality in breast cancer. Material and methods: Review of the database of a cancer center of a University hospital. Patients with infiltrating breast cancer treated between 1997 and 2012 were selected. The pathology type and lymph node involvement were obtained from the pathology report. The expression of estrogen, progesterone and Human Epidermal Growth Factor Receptor 2 (HER2) was determined by immunohistochemistry or in situ fluorescent hybridization (FISH). The absolute peripheral neutrophil and lymphocyte counts were obtained from a complete blood count obtained at least three months before treatment. Patients were followed for a median of 61 months (range 1-171). Results: From 323 eligible patients, after excluding those in stage IV and those without an available complete blood count, 131 patients were analyzed (81 with negative receptors and 117 HER2 enriched). The neutrophil/lymphocyte ratio was similar in both type of tumors (2.1 and 1.91 respectively). Twenty two patients died during follow up. Surviving patients with HER2 enriched tumors had a lower neutrophil/lymphocyte ratio than those who died (1.79 and 3.21 respectively, p < 0.01). In a multivariate analysis, including age, tumor stage and lymph node involvement as confounding factors, the neutrophil/lymphocyte ratio was still significantly associated with a risk of death with a hazard ratio of 2.56. Conclusions: A high neutrophil/lymphocyte ratio in the complete blood count can be a predictor of death in breast cancer.