Postoperative delirium (POD) is an acute change in cognitive status characterized by fluctuating consciousness and is associated with high incidences of morbidity, high complication rates, and long hospitalizations. This study was performed to determine the incidence of POD and the perioperative risk factors in order to predict which patients have an increased risk and thus to prevent POD after major head and neck surgery. The authors retrospectively evaluated 341 patients who underwent laryngectomy or the Commando (combined operation of mouth, mandible, and neck dissection) procedure at Pusan National University Hospital from January 1986 through July 2001. Postoperative delirium developed in 13.8% of the patients who underwent laryngectomy (42 of 304) and 13.5% of the patients who underwent the Commando procedure (5 of 37). A multivariate analysis showed that older age, hypertension, low postoperative O2 saturation, and decreased postoperative hemoglobin levels were risk factors for POD (p < .05). Postoperative delirium is preventable, and its incidence can be decreased by predicting these risk factors during the preoperative and postoperative periods.