BackgroundPostoperative delirium is a serious complication that can occur within the 5th postoperative day. In 2017, the European Society of Anesthesiologists delivered dedicated guidelines that reported the need for routine monitoring using validated scales.ObjectiveAim of this systematic review is to identify clinical studies related to postoperative delirium that included postoperative monitoring with validated scales.DesignSystematic reviewMethodsSearched keywords included the following terms: postoperative, postsurgical, post anesthesia, anesthesia recovery, delirium, and confusion. Two researchers independently screened retrieved studies using a data extraction form.ResultsLiterature search led to retrieve 6475 hits; of these, 260 studies (5.6% of the retrieved), published between 1987 and 2021, included in their methods a diagnostic workup with the use of a postoperative delirium validated scale and monitored patients for more than 24 h, therefore are qualified to be included in the present systematic review.ConclusionIn conclusion, available clinical literature on postoperative delirium relies on a limited number of studies, that included a validated diagnostic workup based on validated scales, extracted from a large series of studies that used inconsistent diagnostic criteria. In order to extract indications based on reliable evidence-based criteria, these are the studies that should be selectively considered. The analysis of these studies can also serve to design future projects and to test clinical hypothesis with a more standardized methodological approach.