Postoperative cognitive dysfunction (POCD) is a decline in cognitive function for weeks or months after surgery. Due to its subtle nature, neuropsychological testing is necessary for its detection. The interpretation of literature on POCD is difficult because of numerous methodological limitations, particularly the different definitions of POCD and the lack of data from control groups. POCD is common after cardiac surgery, and recent studies have now verified that POCD also exists after major non-cardiac surgery, although at a lower incidence. The risk of POCD increases with age, and the type of surgery is also important because there is a very low incidence associated with minor surgery. Regional anaesthesia does not seem to reduce the incidence of POCD, and cognitive function does not seem to improve after carotid surgery as has previously been suggested.