Previous studies have indicated an age effect in the strength of high school wrestlers. The purpose of this investigation was to quantify horizontal abduction and adduction strengths at the shoulder in high school wrestlers and to examine the age effect for these movements. Seventy-nine high school wrestlers (age = 16.28 +/- 1.26 yrs) were stratified into four groups corresponding to the ages of the wrestlers during their freshman, sophomore, junior, and senior years. The subjects were tested for horizontal abduction and adduction strength at the shoulder at 30, 180, and 300 degrees /sec. Body composition was determined from underwater weighing. The results of this study indicated that absolute peak torque and peak torque divided by body weight or fat-free weight increased across age at 30 degrees /sec for abduction and adduction as well as at 180 degrees /sec for adduction. No significant differences in absolute or relative strength across age were noted at 180 degrees /sec for abduction or at 300 degrees /sec for abduction and adduction. These results suggest an age effect for muscular strength development in high school wrestlers that is independent of increases in body weight and fat-free weight. In addition, these results provide normative data for comparisons with other athletes and nonathletes and may be used for assessing readiness to return to activity after in jury. J Orthop Sports Phys Ther 1992;15(4):183-186.