We investigated levels of anticipatory distress in 80 pediatric patients, 2 to 7 years old, awaiting their initial radiation therapy (RT) procedure, and we examined demographic, medical, and psychosocial variables associated with their distress. Both observed behavior and heart rate outcomes were employed as measures of distress. Sixty-five percent of patients exhibited at least some degree of anticipatory behavioral distress prior to their RT simulation procedure. Thirty-four percent of patients displayed high levels of anticipatory behavioral distress; 16.3% exhibited high behavioral distress as well as high heart rates. Younger age and higher parent expectations of child distress were characteristic of children who displayed both high anticipatory behavioral distress and high heart rates. Child demographic factors, particularly younger age, were found to contribute significantly to the prediction of parent expectations of child distress. Implications for at-risk children in need of preparatory interventions for RT procedures are discussed.Radiation therapy (RT) is a commonly used modality to treat pediatric malignancies. RT is used in the primary (alone) or adjuvant (in conjunction with surgery or chemotherapy) setting depending on the tumor type or other factors coincident