Objective: The debate on the value of laboratory tests in the diagnosis of acute appendicitis (AA) continues. In this study, we aimed to evaluate the blood count parameters and the diagnostic value of neutrophil/lymphocyte ratio in the diagnosis of acute appendicitis. Method: 851 patients who underwent appendectomy under emergency conditions were included in the study. Patients were divided into 2 groups; Group 1 was negative appendectomy and Group 2 was acute appendicitis. In addition, they were divided into subgroups as 18-39 years, 40-59 years, and 60 years and older. Neutrophil, platelet, lymphocyte count and Neutrophil/lymphocyte ratio were compared in groups and subgroups. Results: There were 146 patients (17.1%) in Group 1 (negative appendectomy group) and 705 patients (82.9%) in Group 2 (acute appendicitis group). Male sex was dominant in Group 2 (p=0.049). Neutrophil count and neutrophil / lymphocyte ratio (NLR) were higher in Group 2 (p<0.001, p<0.001, respectively), whereas in Group 1, lymphocyte count and platelet count were higher (p=0.008, p=0.002, respectively). The cutoff value for NLR was found to be 5.29 in the ROC curve analysis.