Objective To investigate preoperative PLR and NLR in patients with cholecystitis and to identify a relevant NLR value that discriminates between simple and severe cholecystitis. Methods This study included 280 patients who under went laparoscopic cholecystectomy due to cholecystitis. The Receiver Operating Characteristic (ROC) analysis was performed to identify the most useful PLR cut-off value and NLR cut-off value in relation to the severity of cholecystitis. The patients were divided into two groups according to the cut-off NLR and PLR value. Severe cholecystitis was defined when the cholecystitis was complicated by secondary changes, including hemorrhage, gangrene, emphysema, and perforation. The NLR was calculated at admission as the absolute neutrophil count divided by the absolute lymphocyte count. Results Our study population comprised 212 patients with simple cholecystitis (75.7%) and 68 patients with severe cholecystitis (24.3%). The PLR of 129.0 could predict severe cholecystitis with 86.8% sensitivity and 60.4% specificity. The NLR of 3.0 could predict severe cholecystitis with 82.4% sensitivity and 84.4% specificity. A higher PLR (129) group was significantly associated with severe cholecystitis (P<0.001), higher white blood cell count (P<0.001) and admission via the emergency department (P<0.001). A higher NLR (3.0) was significantly associated with older age (P = 0.039), male gender (P = 0.010), severe cholecystitis (P<0.001), higher white blood cell count (P<0.001), admission via the emergency department (P<0.001) and prolonged length of hospital stay (LOS, P<0.001). Multivariate analysis found that patient age 55 years (OR 2.808,95%CI 1.375-5.735,P = 0.005), white blood cell count 10000 (OR 3.004,95%CI 1.130-7.981,P = 0.027), preoperative NLR 3.0 (OR 9.564,95%CI 4.194-21.812,P<0.001), and admission via the emergency department (OR 2.657,95%CI 1.166-6.054,P = 0.020) were independent factors associated with prolonged LOS. Conclusions PLR 129.0 and NLR 3.0 were significantly associated with severe cholecystitis and prolonged LOS in patients undergoing cholecystectomy. Therefore, preoperative PLR and NLR in patients undergoing cholecystits due to cholecystitis seemed to be a useful surrogate marker for severe cholecystitis.