OBJECTIVE: To compare the effects of shoulder bracing on active joint-reposition sense in subjects with stable and unstable shoulders. DESIGN AND SETTING: Two subject groups, with stable and unstable shoulders, participated in an active joint-reposition test of the shoulder under braced and unbraced conditions. SUBJECTS: Forty subjects (22 men, 18 women; age = 21.85 +/- 3.12 years; height = 173.97 +/- 10.08 cm; weight = 71.27 +/- 11.68 kg) were recruited to participate in this study. Twenty Division I athletes were referred to us for shoulder instability, which was subsequently confirmed with clinical assessment. The remaining 20 subjects were recruited from a similar student population and assessed as having stable shoulders. MEASUREMENTS: Each subject's ability to perceive joint position sense in space was tested by actively reproducing 3 preset angles (10 degrees from full external rotation, 30 degrees of external rotation, and 30 degrees of internal rotation) with and without a shoulder brace. Full, active external-rotation range of motion was assessed before active joint-reposition sense testing. RESULTS: While wearing the shoulder brace, the group with unstable shoulders demonstrated significant improvement in the accuracy of active joint repositioning at 10 degrees from full external rotation in comparison with the stable group. Furthermore, those with unstable shoulders demonstrated significantly less full external rotation than did those with stable shoulders, and the brace reduced full external rotation only for those with stable shoulders. CONCLUSIONS: Our findings suggest that shoulder active joint-reposition sense in subjects with unstable shoulders can be improved at close to maximal external rotation by wearing a shoulder brace. This effect does not appear to be related to restriction of shoulder external rotation.