Postoperative cognitive impairment is a decline in cognitive function that may persist from one to 12 months after surgery, or longer. In some cases, it may persist for several years after major surgery. Postoperative cognitive impairment is different from the onset of delirium. Its causes are under investigation and it typically occurs in older patients and those with pre-existing cognitive impairment. The causes of postoperative cognitive impairment are not understood. It does not appear to be caused by decreased oxygen or blood flow to the brain. It may be mediated by the body's inflammatory response to surgery. Postoperative cognitive impairment is common after cardiac surgery, and recent studies have now demonstrated that postoperative cognitive impairment is also present after major noncardiac surgery, although at a lower incidence. The risk of neurological dementia increases with age, and the type of surgery is also important as there is a very low incidence associated with minor surgery. Postoperative cognitive impairment is common in adult patients of all ages upon discharge from hospital after major noncardiac surgery, but only the elderly are at high risk for long-term cognitive problems. Patients with postoperative cognitive impairment are at increased risk of death in the first year after surgery. Research interest has increased since the early 2000s, especially as more elderly patients are able to undergo successful minor and major surgical procedures. Postoperative cognitive impairment has been studied by several institutions since the inception of the study, which was based in Eindhoven, the Netherlands, and Copenhagen, Denmark. This study found no causal relationship between cerebral hypoxia and hypotension and postoperative cognitive impairment. Age, duration of anesthesia, preoperative complications, and postoperative infections were found to be associated with postoperative cognitive impairment. The body's inflammatory response to surgery is likely to play an important role, at least in elderly patients. Several research initiatives in recent years have evaluated whether measures taken before, during, and after surgery can reduce the potentially harmful effects of inflammation. For example, anti-inflammatory agents can be given before surgery. During surgery, inflammation can be modulated by temperature control, the use of local rather than general anesthesia, or the use of beta-blockers. After surgery, optimal pain management and infection control are important. Several studies have shown positive effects of variable importance when a multidisciplinary, multifactorial approach is taken for the elderly patient during pre-, peri- and postoperative care.