Objective: To examine the incidence and risk factors of early neurological complications after cardiac or aortic surgery using cardiopulmonary bypass technique in King Chulalongkorn Memorial Hospital, Thailand. Materials and Methods: The present study was a retrospective cohort study. Clinical data of adult patients that underwent cardiac or aortic surgery using cardiopulmonary bypass technique in 2018 were reviewed from the electronic medical record in the authors’ center. Results: Early postoperative neurological complications occurred in 33 (8.3%) of the 400 patients. Twenty of them (60.6%) had non-specific encephalopathy, three (9.1%) had hypoxic-ischemic encephalopathy, five (15.2%) had provoked seizure, four (12.1%) had cerebral infarction, and one (3.0%) had intracranial hemorrhage. Associated clinical factors included history of essential hypertension [adjusted odds ratio 3.448 (95% CI 1.266 to 9.391)], combined coronary artery bypass grafting and valve surgery [adjusted odds ratio 4.759 (95% CI 1.182 to 19.170)], multi-valve surgery [adjusted odds ratio 5.201 (95% CI 1.227 to 22.049)], aortic surgery [adjusted odds ratio 17.260 (95% CI 4.168 to 71.468)], higher midazolam dosage [adjusted odds ratio 1.009 (95% CI 1.002 to 1.015)], higher serum lactate prior to discontinuing cardiopulmonary bypass [adjusted odds ratio 1.263 (95% CI 1.093 to 1.460)], and presence of intraoperative intra-aortic balloon pump use [adjusted odds ratio 6.160 (95% CI 1.883 to 20.150)]. Conclusion: Early postoperative neurological complications rate of cardiac or aortic surgery using cardiopulmonary bypass technique in the present study settings was 8.3%. Preoperative and intraoperative clinical factors associated with such complications were the history of essential hypertension, the type of surgery such as combined coronary artery bypass grafting and valve surgery, multi-valve surgery, and aortic surgery, the higher midazolam dosage, the higher serum lactate prior to discontinuing cardiopulmonary bypass, and the presence of intraoperative intra-aortic balloon pump use. Keywords: Cardiac surgery; Aortic surgery; Cardiopulmonary bypass; Postoperative neurological complications; Encephalopath