Objective: Acute appendicitis (AA) is the most common cause of intra-abdominal surgery worldwide and its diagnosis continues to be problematic despite advancedtechnology and diagnostic methods. Easily accessible, economical and non-invasive tests are still under investigation for the diagnosis and after surgery. The purposeof this study was to review postoperative changes in patients’ complete blood count (CBC) parameters.Methods: The research was performed as a single-center, retrospective, cross-sectional study. After obtaining the approval of the ethics committee, the data obtainedfrom patients aged over 18, who underwent appendectomy between January 1, 2015 and November 30, 2017, and who were diagnosed with histopathologicallyconfirmed AA, were retrospectively examined. Wilcoxon test was used in statistical analysis to compare pre- and post-operative changes in CBC parameters. A p value ofless than 0.05 was considered statistically significant.Results: Men constituted 50% (n=726) of the 1452 enrolled patients. The mean age of the patients was 32.3±16.1 years. Statistically significant differences weredetermined between pre-operative and post-operative leukocyte white blood cell, lymphocyte, hemoglobin, hematocrit, plateletcrit and mean platelet volume values.Mean neutrophil and platelet count values decreased in the post-operative period, although these decreases were not statistically significant. No statistically significantdifference was determined between pre-operative and post-operative neutrophil/lymphocyte ratio (NLR) values.Conclusion: Dilutional changes in CBC parameters may occur following fluid therapy in the post-operative period. We also conclude that NLR is not affected by fluidtreatment and may be a valuable parameter in monitoring post-appendectomy infection.