Teleroentgenograms of the upper extremity in 244 children (123 boys and 121 girls) were made at six-month intervals from the age of seven to the time of skeletal maturity. Lengths were measured to determine the growth remaining at both growth plates of the humerus, radius, and ulna. The subjects were healthy, well nourished, middle-class Americans, mostly of northwest European descent. After the age of seven, the proportion between the upper and lower arms does not change appreciably. The humerus is 18 per cent of standing height in girls at the age of seven and 19 per cent at the age of fifteen. In boys, the humerus is 18 per cent of standing height at the age of seven and 20 per cent at the age of seventeen. The length of the radius is 13 per cent of standing height in girls at the age of seven, increasing to 14 per cent by skeletal maturity. In boys, the length of the radius increases from 14 per cent of standing height at the age of seven to 15 per cent at skeletal maturity. From the age of seven to skeletal maturity, the humerus grows approximately 1.2 centimeters in girls and 1.3 centimeters in boys each year. In girls, the ulna grows approximately 1.0 centimeter and the radius, 0.9 centimeter each year after the age of seven. In boys, the ulna grows approximately 1.1 centimeters and the radius, approximately 1.0 centimeter each year from the age of seven to skeletal maturity. Based on these data, accurate predictions of growth and of growth discrepancy in the upper extremity can be made, and the time at which to perform equalization procedures can be determined more precisely.