Prediction of postoperative complications (POC) is an important element in the choice of treatment tactics for acute peritonitis (AP). Many methods have been proposed for this. However, none of these methods have sufficient recognition. Most prognostic scales determine the risk of complications only after surgery. Therefore, the issue of developing an informative prognostic scale remains relevant.The aim of the study was to evaluate prognostic factors in patients with acute peritonitis.Materials and Methods. Retrospective analysis of the results of treatment of 212 patients with AP. 65 patients had POC. 22 patients died. Analysis of clinical, anthropometric data, laboratory examination results, criteria of MPI, PIPAS, WSES Sepsis Severity Score (WSSS), Charlson Comorbidity Index (CCI) was performed. Analysis of Variance (ANOVA) and Neural Network Bayesian Classifier were used to assess the influence of factors.Results. None of the studied criteria is sufficient for prediction. MPI, PIPAS, WSSS have the greatest influence on the probability of POC occurrence in AP. But these indicators can be determined only after the operation. Therefore, we separately used a cumulative assessment of indicators that can be determined before surgery and after surgery. Multifactor ANOVA with preoperative parameters: diagnosis, clinical signs of AP, body temperature, CCI, systolic blood pressure (SBP) showed that since 5 P-values are less than 0.05, combination of these factors have a statistically significant effect on POC at the 95.0% confidence level. Multifactor ANOVA with indicators of diagnosis, body temperature, CCI, SBP, WSSS or PIPAS showed that since 5 P-values are less than 0.05, combination of these factors have a statistically significant effect on POC at the 95.0% confidence level.Conclusions 1. Criteria MPI, PIPAS, WSSS have the greatest influence on the probability of POC occurrence in AP, but none of these criteria is sufficient alone. 2. The set of indicators of diagnosis, clinical signs of peritonitis before surgery, body temperature, CCI, SBP have a statistically significant effect on POC at the 95.0% confidence level before surgery. 3. The combination of indicators of diagnosis, body temperature, CCI, SBP, WSSS or PIPAS have a statistically significant effect on POC at the 95.0% confidence level after surgery. 4. The creation of a reliable prognostic scale is possible using a complex of the described factors.