Aim: Preliminary evidence suggests that inflammation plays a role in the development and prognosis of pulmonary embolism (PE). We used the neutrophil/lymphocyte ratio (NLR) as a measure of systemic inflammation and investigated its association with PE. Materials and methods: A total of 266 patients who were diagnosed with PE and a control group of 124 age- and sex-matched healthy subjects were included in this study. We further classified the PE patients into 2 groups: those who survived and those who died in the first 30 days. Baseline NLR was measured by dividing neutrophil count to lymphocyte count and was compared between the groups. Results: Median NLR was significantly higher among patients with PE compared to the healthy control group (3.9 (interquartile range (IQR): 5.0) vs. 1.9 (IQR: 0.6), P < 0.001). Of the 266 patients with PE, 16 (6%) died within 1 month. Median NLR was significantly higher among PE patients who died compared to those who survived, as well (3.7 (IQR: 4.3) vs. 9.0 (IQR: 7.9), P < 0.001). The optimal cut-off values, sensitivities, and specificities of NLR for predicting PE and in-hospital mortality of PE were >2.565 and >5.465, 70.3% and 75.0%, and 92.7% and 67.6%, respectively. Multiple logistic regression analysis showed that NLR values of >5.465 could define those patients with a mortal clinical course independently (odds ratio: 13.446, 95% confidence interval: 3.141 57.566, P < 0.001). Conclusion: A higher NLR, as an emerging marker of inflammation, may be beneficial in determining prognosis in PE patients.