Based on previous studies, we hypothesized that the clinical phenomena of preoperative anxiety, emergence delirium, and postoperative maladaptive behavioral changes were closely related. We examined this issue using data obtained by our laboratory over the past 6 years. Only children who underwent surgery and general anesthesia using sevoflurane/O(2)/N(2)O and who did not receive midazolam were recruited. Children's anxiety was assessed preoperatively with the modified Yale Preoperative Anxiety Scale (mYPAS), emergence delirium was assessed in the postanesthesia care unit, and behavioral changes were assessed with the Post Hospital Behavior Questionnaire (PHBQ) on postoperative days 1, 2, 3, 7, and 14. Regression analysis showed that the odds of having marked symptoms of emergence delirium increased by 10% for each increment of 10 points in the child's state anxiety score (mYPAS). The odds ratio of having new-onset postoperative maladaptive behavior changes was 1.43 for children with marked emergence status as compared with children with no symptoms of emergence delirium. A 10-point increase in state anxiety scores led to a 12.5% increase in the odds that the child would have a new-onset maladaptive behavioral change after the surgery. This finding is highly significant to practicing clinicians, who can now predict the development of adverse postoperative phenomena, such as emergence delirium and postoperative behavioral changes, based on levels of preoperative anxiety.