A prospective 5 years' neuropsychological, neurological, cardiological and electroencephalographical follow-up study was carried out in 44 patients who had undergone open-heart surgery for valve replacement. A distinct interrelationship was found between the clinical outcome immediately after operation and the neuropsychological long-term course despite the rapid recovery of occasional clinical disorders related to operative procedures. In fact, the psychometric performance scores of those who did not develop clinical signs of cerebral dysfunction induced in operation showed a significant difference only years after operation. Similarly, the harmful effects of long perfusion time (extracorporeal circulation) in operation were reflected in the long-term neuropsychological performance. Some evidence seemed to suggest that the correction of the prolonged circulatory disorder might possibly afford real enhancement of higher cerebral functions. The long-term results not only emphasize the importance of a careful clinical evaluation but also emphasize the necessity of considering the subclinical level of events both before and after operation when assessing the overall outcome and cerebral safety of cardiac surgery patients.