Aims: Acute inflammatory processes are associated with perioperative complications.Neutrophil/lymphocyte ratio (NLR) and platelet/lymphocyte ratio (PLR) were reported tohave prognostic importance in various diseases. We aimed to investigate the clinicalimportance of preoperative (preop) and postoperative (postop) NLR and PLR aspredictors of morbidity and surgical or nonsurgical complications after major abdominalsurgery.Methods: Patients who had a major abdominal surgery were retrospectively evaluated.Age, gender, American Society of Anesthesiologist (ASA) score, and the type of operationwere recorded. Preop and postop days 1, 3 and 5 white blood cell (WBC), neutrophil,lymphocyte and platelet counts, duration of intensive care unit stay and hospitalization,Clavien Dindo classification, and surgical or non-surgical complications were determined.Results: The study included 462 subjects. Concerning increased need for red bloodcell transfusions, NLR was significantly higher on postop day 3 but lower on day 5, andPLR was higher on postop day 1 compared to preop state. Regarding a worse ClavienDindoclassification, NLR was higher on postop day 3 but lower on day 5, and PLR washigher on postop day 1 and 3 compared to baseline. In those with increased surgicalcomplications, NLR was lower on postop day 5, and postop day 1 and 3 PLR were highercompared to baseline values. In subjects with higher non-surgical complications, NLRwas higher on postop day 3 but lower on day 5 compared to preop measurements. PLRwas similar across the days of follow up in terms of non-surgical complications.Conclusions: Higher NLR on postoperative day 5, and higher PLR on postoperativedays 1 and 3 compared to preop values were the indicators of increased complicationsin this study.