Light changes in mental function after operation occur in patients of all ages, but more frequent they are observed in older patients. The incidence of early postoperative cognitive dysfunction varies depending on surgical procedure and may be as high as 20-90% in aged patients, and occurs most often in patients undergoing cardiovascular surgery. Early postoperative cognitive dysfunction is a predictor of late postoperative cognitive dysfunction. Delirium develops in at least 50% of older surgical patients and even more frequently after cardiac surgeries (72%). Postoperative delirium, like delirium manifesting with co-existing disease, and late postoperative cognitive dysfunction are strong predictors of functional and cognitive decline in one-year period after discharge and are associated with higher morbidity and mortality, longer hospital stay, and a higher rate of institutionalization. The reasons of postoperative cognitive dysfunction and delirium are not well understood. An assessment of cognitive function should be completed as a routine in older patients, and effective prevention requires the identification of risk factors for delirium: advanced age, preexisting dementia and depression, visual and hearing impairment, Parkinson disease, emergency operation, anticholinergic drugs, and others. After operation, elderly patients must be carefully monitored for probable postoperative delirium. It is important to deepen health care professionals' knowledge of postoperative cognitive complications in older surgical patients.