Objective: The purpose of this study was to evaluate the influence of a posture-cuing shirt on internal rotation velocity of the shoulder during a tennis swing and to determine this influence on shoulder external rotation position. Methods: Nine healthy competitive college tennis players from a Division III college participated in this study. High-speed motion capture allowed for 3-dimensional analysis of shoulder kinematics during a tennis serve. Two conditions were evaluated while the athletes performed a high-velocity tennis serve: a standard tennis shirt and a posture-cuing shirt. Results: Shoulder internal rotation velocity increased when wearing the posture-cuing shirt. Peak internal rotation velocity increased from 960.61°/s ± 93.24°/s to 1217.96°/s ± 155.01°/s (t = -1.76, P = .058). Internal rotation velocity at the time of impact increased from 765.18°/s ± 95.48°/s to 900.54°/s ± 105.33°/s (t = -1.50, P = .086). Shoulder maximum external rotation did not differ between the 2 conditions, at 172.00°± 2.92°and 170.89°± 3.70°(t = 0.325, P = .754). Conclusions: Wearing a posture-cuing shirt may possibly alter shoulder kinematics during an overhead sport activity such as tennis. Internal rotation velocity seemed to improve while wearing this shirt, although shoulder external rotation position did not change. It is not known if these improvements can influence injury risk. (J Chiropr Med 2017;16:49-53)