Serious complications involving the central nervous system in the course of cardiac surgical procedures have become rare. Nevertheless, CNS dysfunctions still are observed in a considerable number of patients, exceeding by far the number of those at risk from preoperative neurological hazards. The influence of extracorporeal circulation performance and hypothermia on the physiology of cerebral autoregulation, as well as microembolization events seem to be crucial factors in this context. The resulting regional or global posthypoxic changes in brain metabolism may lead to the manifestation of various neurologic and psychiatric disorders in the postoperative course. These often minor disturbances of CNS function can only be detected regularly and diagnosed correctly in a prospective way by consulting specialists in neurology, psychiatry and psychology, as performed at the Department of Thoracic- and Cardiovascular Surgery of the University Hospital in Hamburg since 1974, and currently in use an international multicenter study. We found postoperative neurological abnormalities in more than 50% of our patients. While irreversible brain damage occurred in only 0.5% of cases, about twothird exhibited transient symptoms that were no longer apparent after 8-10 days postoperatively. Obvious psychopathological symptoms were noted in 10% of cases after surgery, and minor, likewise transient, psychiatric disturbances were seen in up to 50% of patients; 20% suffered from long-lasting psychic problems. The subjective complaints in these cases exceeded the results of objective assessments to a remarkable amount. The discussion focuses on a critical valuation of clinical and supplementary examination techniques and on the potential pathophysiologic mechanisms induced by extracorporal circulation.