Elbow flexion in hemiplegic cerebral palsy causes not only a functional impairment but is also a cosmetic concern. We report on the natural history of arm positioning during walking at different ages. One hundred seventy-five children (mean age +/- SD, 9.2 +/- 4.1 years) were assessed by using 3-dimensional gait analysis. The results showed a significant spontaneous decrease of elbow flexion on the hemiplegic side with increasing age (P=0.001) and no change on the non involved side. The elbow extension significantly increased on the hemiplegic side (P=0.017) and on the non involved side (P=0.012). The range of motion did not improve significantly on the hemiplegic side, but did on the non involved side (P=0.003). Inasmuch as the hemiplegic side starts out with more flexion at a young age compared with the non involved side, the improvement in extension is not as great as on the non involved side, and there is no marked gain in range of motion.A decreased variability was noted, measured as SDs of the mean elbow flexion, although it was only significant on the non involved side (P=0.008). Comparing a subgroup of 10 patients who had surgical treatment involving the lengthening of the elbow flexors with a nonoperative group of 59 patients, we found that surgery did not contribute to a better positioning of the arm nor did it normalize the movement pattern while walking. Surgical treatment has been proposed to improve the function and the appearance of the posturing arm in hemiplegic cerebral palsy; however, improvement might be expected spontaneously, and the indication and timing of surgical intervention is not clear.