Objective:Despite various pain management methods, chronic pain is still a challenging issue after thoracotomy. This retrospective study was designed to determine the possible factors affecting the development of chronic pain following open thoracotomy.Methods:The study included patients who underwent elective open thoracotomy at Ankara University İbni Sina Hospital, between 01.01.2016 and 31.12.2020. The medical files and electronic records of the patients were scanned from the system. Patient history, analgesic methods, and surgical details were recorded. The need for and usage analgesic drugs after the surgery were also recorded.Results:A total of 229 patients who underwent thoracotomy were included in the study, and 83 (36.2%) patients had chronic pain. Duration of surgery, doses of remifentanil, fentanyl or NSAI drugs, duration or number of chest tubes (more than 4 days, or more than 2 tubes), diabetes, or PCEA usage were found as variables affecting pain. Logistic Regression, Multilayer Perceptron, Naive Bayes, AdaBoost, and Random Forest methods were used to evaluate the prediction performances. According to the model created with logistic regression, the rate of the correct classification was 90.8%. The duration of surgery, remifentanil administration, chest tube for more than 4 days, and diabetes were found to be risk factors for developing chronic pain. Fentanyl bolus, PCEA-bupivacaine, and NSAID bolus were determined as preventive factors.Conclusion:A careful analysis of risk factors should be performed for each patient to prevent chronic pain after thoracotomy, and preemptive effective analgesia methods should be performed.