The purpose of this study was to assess the magnetic resonance imaging (MRI) and clinical outcome after tendon transfers about the shoulder in children with residual brachial plexus birth palsy. Twenty-three children with an average age at surgery of 5.3 +/- 1.7 years underwent transfer of the latissimus dorsi and teres major to the posterior rotator cuff with or without concomitant musculotendinous lengthenings. Preoperative MRI revealed glenoid retroversion measuring -25.3 +/- 14.3 degrees and only 29.5 +/- 15.5% percent of humeral head anterior to the middle of the glenoid. Clinical evaluation showed significant improvements in external rotation and abduction. Postoperative MRI 1 year after surgery revealed no change in glenoid retroversion (-24.5 +/- 14.2) or percent of humeral head anterior to the middle of the glenoid (28.4 +/- 14.9%). These results demonstrate that tendon transfers improve overall shoulder motion but do not reduce humeral head subluxation or enhance glenohumeral joint realignment.