The high incidence of overuse shoulder injuries in elite junior tennis players is often attributed to both the high repetitive stresses inherent in the game, as well as muscular imbalances in the humeral rotators. The purpose of this study was to isokinetically measure concentric glenohumeral joint internal and external rotation strength, to develop a bilateral descriptive profile in elite junior tennis players across two age ranges. One hundred forty seven elite junior players between the ages of 12 and 21 were bilaterally tested on a Cybex isokinetic dynamometer with 90 degrees of abduction. Players were analysed in two groups (12-17 and 18-21 years of age), using isokinetic variables of peak torque and work relative to body weight. Data analysis consisted of ANOVAs, with dependent t-tests used for post-hoc testing where main effect differences were identified. Results indicated no significant main effect difference in the isokinetic relative parameters between the two age groups (p > .01). Significantly greater (p < .001) dominant arm internal rotation was measured in both groups for both males and females, with no significant difference in external rotation strength measured between extremities in either age group. These data show specific adaptations in shoulder strength and identify a relative muscular imbalance between the internal and external rotators on the dominant arm of elite junior tennis players. Normative data presented in this study can assist clinicians and researchers in interpreting isokinetic test results in elite junior tennis players.