OBJECTIVE: To define the incidence, the prognosis, and the risk factors of neurologic complications of open heart surgery. Background. Open heart surgery poses many hemodynamic, embolic, and metabolic threats to the brain with multiple factors relating to neurologic complications. Despite the progress in surgical technique, neurologic complications remain major causes of morbidity and occasional mortality. METHODS: Data were obtained from the charts of 297 patients submitted to open heart surgery at SNUH in 1993. We analysed the risk factors for CNS complications and identified the incidence, the type, and the results of the complications. RESULTS: Among 297 patients, CNS complications occurred in 34 patients(11.4%). The incidences of each complication were as follows. ; 6 anoxic encephalopathies(17.7%), 12 encephalopathies of uncertain etiology(35.3%), 7 seizures (20.6%), 6 TIAs or. Infarctions(17.7%), and 3 other complications(8.8%). Of the 34 patients, there were 6 deaths (17.7%), 1 vegetative state(2.9%), 1 major neurologic deficit(2.9%), 3 minor neurologic deficits(8.8%), and full recovery in 23 patients(67.7%). The risk factors such as age, presence of thrombi, type of operation, duration of bypass, duration of aortic clamping time, use of total circulatory arrest, re-operation, and use of ventricular assist device were statistically significant. CONCLUSION: The CNS complications of open heart surgery are infrequent but still remain important causes of morbidity and mortality. Evaluating the risk factors could be of help to prevent the CNS complications.