['Postoperative delirium and cognitive decline are common in elderly surgical patients after non-cardiac surgery. Despite this prevalence and clinical importance, no specific aetiological factor has been identified for postoperative delirium and cognitive decline. In experimental setting in a rat model, nitrous oxide (N(2)O) produces neurotoxic effect at high concentrations and in an age-dependent manner. Whether this neurotoxic response may be observed clinically has not been previously determined. We hypothesized that in the elderly patients undergoing non-cardiac surgery, exposure to N(2)O resulted in an increased incidence of postoperative delirium than would be expected for patients not receiving N(2)O.', 'Patients who were >or=65 yr of age, undergoing non-cardiac surgery and requiring general anaesthesia were randomized to receive an inhalational agent and either N(2)O with oxygen or oxygen alone. A structured interview was conducted before operation and for the first two postoperative days to determine the presence of delirium using the Confusion Assessment Method.', 'A total of 228 patients were studied with a mean (range) age of 73.9 (65-95) yr. After operation, 43.8% of patients developed delirium. By multivariate logistic regression, age [odds ratio (OR) 1.07; 95% confidence interval (CI) 1.02-1.26], dependence on performing one or more independent activities of daily living (OR 1.54; 95% CI 1.01-2.35), use of patient-controlled analgesia for postoperative pain control (OR 3.75; 95% CI 1.27-11.01) and postoperative use of benzodiazepine (OR 2.29; 95% CI 1.21-4.36) were independently associated with an increased risk for postoperative delirium. In contrast, the use of N(2)O had no association with postoperative delirium.'] Does nitrous oxide change the incidence of postoperative delirium or cognitive decline in elderly surgical patients?