Objective: The aim of this study is to assess the diagnostic value of the neutrophil-to-lymphocyte ratio in the differential diagnosis of patients with vaginal bleeding related to ectopic pregnancy or miscarriage. Study design. A retrospective analysis of case histories of patients with documented ectopic pregnancies or miscarriages diagnosed by a combination of clinical examination, transvaginal ultrasonography, and human chorionic gonadotropin assay. Normal pregnant women were used as controls. The neutrophil-to-lymphocyte ratio was calculated in the patients and controls. Results: The neutrophil-to-lymphocyte ratio was higher in patients with ectopic pregnancies than in patients with normal pregnancies or patients with miscarriages (P<0.05). Although the neutrophil-to-lymphocyte ratio in patients with miscarriages was higher than that in patients with normal pregnancies, the difference was not statistically significant. For ectopic pregnancy, using 3.0 as a cutoff value, the sensitivity and specificity of the neutrophil-to-lymphocyte ratio were 61%. For miscarriage, using 2.8 as a cutoff value, the sensitivity and specificity of neutrophil-to-lymphocyte ratio were 53%. Conclusions: In patients with vaginal bleeding related to ectopic pregnancy or miscarriage, an increased neutrophil-to-lymphocyte ratio in the absence of infection may be used as an early diagnostic marker for ectopic pregnancy. Miscarriage did not result in a significant increase in the neutrophil-to-lymphocyte ratio. Further studies performed in patients grouped by gestational age and rupture status are needed to determine the diagnostic value of the neutrophil-to-lymphocyte ratio in patients suspected of an ectopic pregnancy.