We evaluated the results of shoulder-strengthening exercises with our novel shoulder orthosis to stabilize the scapula in 46 patients with multidirectional shoulder instability. We quantified the changes in muscle strength produced by our rehabilitation program. Our study included 34 female patients and 12 male patients (mean age, 20 years) with 73 affected shoulders. All patients performed the prescribed exercise program for 8 weeks. Their mean total scores on the modified Rowe grading system significantly increased from 51.9 to 74.9 points (P <.001). The mean peak torque of internal and external rotation, measured with an isokinetic dynamometer, significantly increased (P <.05); the mean external/internal peak torque ratios significantly decreased (P <.05) and were normalized upon completion of the rehabilitation program. Because of failure of conservative treatment, 3 patients underwent surgery at a mean follow-up duration of 7 years. We conclude that the prescribed shoulder-strengthening exercise represents a useful treatment option for patients with multidirectional shoulder instability.