Findings from a study of 47 children between 3.5 and 12 years of age who received tonsillectomies at a children's hospital are presented. During a home visit before hospitalization, the child's adjustment, cognition, temperament, and family characteristics were assessed. Tonsillectomies were followed by an overnight stay at the hospital, and behavioral ratings were made during that period. One to two weeks after the child returned home, the mother again completed measures of the child's adjustment. Findings indicated that adjustment prior to hospitalization was the strongest predictor of post-surgical adjustment. However, cognitive, temperamental, and family factors were also significant predictors. Children's conceptualizations of illness and medical procedures were strongly related to general cognitive development, and more sophisticated illness conceptualizations were associated with better adjustment after surgery. Children who displayed the most positive reactions to hospitalization were temperamentally more rhythmical, i.e., had predictable, regular behavior, and tended to be more approaching to new experiences. They were also more adaptable, more positive in mood, more distractible, and had lower thresholds of responsiveness. Measures of family characteristics were less strongly associated with children's reactions to hospitalization. However, maternal anxiety, overprotection, and overindulgence were predictive of poorer adjustment. (Author)