Objective measurement of range of motion of the glenohumeral joint is important for the rehabilitation and prevention of shoulder injury. The primary purpose of this study was to determine whether significant differences exist between the dominant (tennis playing) and nondominant extremity in active internal and external rotation range of motion in elite junior tennis players 11-17 years of age. Two hundred three elite junior tennis players (113 males, 90 females) were bilaterally measured for internal and external rotation at 90 degrees of abduction in a supine position with a specific methodology attempting to isolate glenohumeral motion, while minimizing or negating scapulothoracic motion. A standard universal goniometer was utilized to measure active range of motion (AROM). Dependent t tests were used to compare differences between extremities. No significant difference was found for males or females between the dominant and nondominant arm in external rotation. Analysis of internal rotation (AROM) differences showed significantly less (p < .001) internal rotation (AROM) on the dominant arm for both males and females. Significantly less (p < .001) dominant arm total rotational range of motion was also found in both males and females. The loss of dominant arm internal rotation (AROM) has clinical application for both the development of rehabilitation and preventative flexibility/range of motion programs.