Sixty-five families were enlisted in a study exploring factors associated with distress behavior in 5-year-old children receiving diphtheria-tetanus-pertussis immunizations. At a home visit 1 month before the immunization, the following measures were obtained: (1) the Behavioral Style Questionnaire, a measure of temperament: (2) parental self-reports of medically related attributes (eg. "good patient"); (3) parental attitudes toward pain in children and responsiveness to their child's pain; and (4) parental prediction of distress at upcoming immunization. The child's distress behavior during the immunization was evaluated using a modification of the Procedure Rating Scale-Revised and, after the procedure, the child's assessment of his or her pain was elicited using the Oucher. Children's mean Procedure Rating Scale-Revised score was 2.57 of a possible 11. Thirty-one (48%) had low (less than or equal to 1) and 7 (11%) had high distress scores (greater than or equal to 2 SD above the mean). Factors positively correlated with distressed behavior included more "difficult child" cluster characteristics, the individual temperamental dimension of adaptability, but few parental attitudes and attributes. Parent's predictions of distress were the strongest correlates. These findings document the variation that children demonstrate in response to pain and offer some insight into associated innate and environmental factors. These results imply that treatment strategies derived from parental knowledge and tailored to individual characteristics of the child may be most effective in alleviating pain-related distress in medical settings.