Objective: To determine predictors and behavioral outcomes of preoperative anxiety in children undergoing surgery. Design: A prospective, longitudinal study. Setting: A university children's hospital. Participants: One hundred sixty-three children, 2 to 10 years of age (and their parents), who underwent general anesthesia and elective surgery. Main Outcome Measures: In the preoperative holding area, anxiety level of the child and parents was determined using self-reported and independent observational measures. At separation to the operating room, the anxiety level of the child and parents was rated again. Postoperative behavioral responses were evaluated 3 times (at 2 weeks, 6 months, and I year). Results: A multiple regression model (R(2)=0.58, F=6.4, P=.007) revealed that older children and children of anxious parents, who received low Emotionality, Activity, Sociability, and Impulsivity (EASI) ratings for activity, and with a history of poor-quality medical encounters demonstrated higher levels of anxiety in the preoperative holding area. A similar model (R(2)=0.42, F=8.6, P=.001) revealed that children who received low EASI ratings for activity, with a previous hospitalization, who were not enrolled in day care, and who did not undergo premedication were more anxious at separation to the operating room. Overall, 54% of children exhibited some negative behavioral responses at the 2-week follow-up. Twenty percent of the children continued to demonstrate negative behavior changes at 6-month follow-up, and,in 7.3% of the children these behaviors persisted at 1-year follow-up. Nightmares, separation anxiety, eating problems, and increased fear of physicians were the most common problems at 2-week follow-up. Multivariate analysis demonstrated that child's age, number of siblings, and immediate preoperative anxiety of the child and mother predicted later behavioral problems. Conclusions: Variables such as situational anxiety of the mother, temperament of the child, age of the child, and quality of previous medical encounters predict a child's preoperative anxiety. Although immediate negative behavioral responses develop in a relatively large number of young children following surgery, the magnitude of these changes is limited, and long-term maladaptive behavioral responses develop in only a small minority.