We studied the effect of preoperative preparation on stress reduction in children hospitalized for dental surgery under general anesthesia. Participants were 45 children, 3 and 4 years of age, with no previous hospital-surgery experience and no history of medical or psychological conditions requiring special care. Subjects were randomly assigned to one of three experimental groups: control, receiving no preoperative preparation; unrelated play therapy, receiving a preoperative play session unrelated to hospital or surgical procedures; and related play therapy, receiving a preoperative play session focusing on hospital and surgical procedures. Subjects' behavior was assessed using behavior observation scales for cooperation and upset at seven stress points: admission, nurse's examination, pediatric medical examination, blood test, preoperative injection, transfer to surgery, and induction. The related play therapy group was more cooperative and less upset than either the unrelated play therapy group or the control group across stress points. No significant heart rate differences were found among the three groups. The results suggest that play therapy related to hospital and surgical procedures can alleviate stress and anxiety in 3- and 4-year-old children.