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The objective of this article was to estimate the incidence of delirium in a sample of patients undergoing elective surgery and to identify the preoperative factors most closely associated with developing this complication. Consecutive patients (n=500) underwent a full preoperative medical evaluation including assessment of cognitive and functional status. Daily evaluation on postoperative days 1 through 4 included medical record review and direct standardized patient interviews. Logistic regression was used to explore the associations between preoperative factors and postoperative delirium. Delirium was detected in 57 (11.4%) patients. Univariate factors associated with delirium included age> or =70 years (RR=3.1 [1.75,5.55]), preexisting cognitive impairment (RR=3.1 [1.73, 5.43]), greater preoperative functional limitations (RR=1.57 [1.27, 1.94]), and a history of prior delirium (RR 4.1 [1.98 to 8.27]. Adjusting for other factors, previous delirium (OR=4.08 [1.85, 9.0]), age> or =70 years (OR=3.2 [1.6, 6.0], and preexisting cognitive impairment (OR=2.16 [1.15, 4.0] remained predictive of delirium. Patients' perceptions that alcohol had affected their health (OR=6.53 [1.58 to 28.1]) and use of narcotic analgesics just prior to admission (OR=2.7 [1.37 to 5.3]) were also significantly associated with delirium postoperatively. Several easily obtained preoperative clinical factors can be used to identify patients at risk for postoperative delirium. This approach, when combined with specialized delirium teams using established guidelines, may be more effective in targeting patients at risk, thus reducing the number of episodes and days of delirium.