The objective of this study was to determine the influence of rotational muscle strength on shoulder function after a combined open Bankart and modified Bristow procedure and to determine the time of recovery for shoulder rotational strength. Fourteen patients were investigated by use of the relationship between the Rowe score and isokinetic concentric muscle strength. Forty patients were measured regarding the time course of muscle strength preoperatively and at 1.5, 3, 4.5, 6, 9, and 12 months postoperatively. There was a positive correlation coefficient between the Rowe score and muscle strength. The mean peak torque was significantly lower than the preoperative level at 1.5 and 3 months after surgery (P < .01) and recovered by 4.5 months after surgery. The contralateral peak torque ratio continued to increase until 12 months after surgery. These results indicate that high-level sports activities should be delayed until 9 to 12 months after a Bankart and modified Bristow procedure.