A strong perception exists that elderly people are at risk for persistent cognitive deterioration lasting longer than six months following major surgery, particularly heart surgery. Furthermore, based on laboratory evidence, investigators hypothesize that surgery or anesthesia might precipitate incident dementia. Recent clinical studies have found that cognition might frequently be impaired within the first few months postoperatively, and that such impairment may be associated with death or debility. Unsurprisingly, the specter of cognitive decline or dementia following surgery is a source of consternation to elderly people and their families. However, there are methodological concerns relating to the investigation of postoperative cognitive decline. Studies have been hampered by lack of standard diagnostic criteria for cognitive decline, by the use of statistical rather than clinical definitions, by poorly matched controls or even the absence of controls, and by inadequate detection of preexisting mild dementia. For these reasons, there are ongoing controversies surrounding the time course, the severity, and even the clinical relevance of persistent postoperative cognitive deterioration. There is evidence that most patients recover cognition in the long-term, and that for those who experience persistent decline, this is probably attributable to underlying undiagnosed neurological disease or other co-morbidities rather than to surgery or to anesthesia. There is currently minimal clinical evidence linking surgery or anesthesia to incident dementia. Rigorous clinical research is needed to resolve the controversy whether anesthesia or surgery is likely to cause persistent neurological decline or to precipitate dementia.