Delirium is a common but often undiagnosed complication in the elderly following a major operation. Recognizing the presentation of delirium and the criteria to establish the diagnosis of delirium will improve a clinician's ability to detect this complication. Treating delirium with environmental, supportive, and pharmacologic interventions reduces the incidence and side effects of postoperative delirium. The purpose of this review is to describe the diagnosis and treatment of postoperative delirium.