The nature of children's distress reactions to medical treatment is examined in terms of age and sex differences and initial normative data are provided. Predominately white, middle class children, ages 1 to 11, were observed while receiving allergy treatment injections. Males were observed on 453 injection occasions while females were observed on 259 injection occasions making a total of 712 observations. Unobtrusive observations were made in the waiting room over a 7-week period. Observers marking rating sheets were able to be unobtrusive because (1) there were 10 to 20 adults in the waiting room at any one time and (2) many of these people read or worked while waiting. Data were collected with the Child Medical Distress Scale which scores 12 aspects of children's expression of distress as well as yielding a total scale score. Results indicated that, in general, children between the ages of 4 to 5 years and younger displayed substantially more overt indicators of distress than children of 7 to 11 years of age. The data show that "grimacing,""affected posture," and "overall distress" occurred most often in all children and that "pain statements" and "steps away" occurred least often. On many items there were substantial changes in score across age. Implications for understanding children's responses to medical treatment are discussed and a copy of the rating scale employed as well as figures depicting mean performance on each item of the scale for both sexes across age are included in the report. (Author/RH)