The implementation of new markers of bacterial infection into clinical practice is hindered by their costs. We assessed the potential use of the neutrophil to lymphocyte count ratio (NLCR) to discriminate between bacterial and viral infections. NLCR was evaluated in 45 patients with bacterial infections: 24 patients with viral infections and 18 healthy adults. The medians of NLCR were 11.73 in bacterial infections, 2.86 in viral infections and 1.86 in controls. The NLCR cut-off value of 6.2 exhibited a sensitivity value of 0.91 and a specificity value of 0.96 for bacterial infection. These results suggest a diagnostic potential for NLCR.