Aim: To investigate the natural history and the impact of reconstruction in shoulder deformities due to obstetrical brachial plexus palsy. Methods: Pre and postoperative CT scans of bilateral upper extremities of 28 patients with obstetrical palsy were studied. The age during the preoperative CT scan ranged from 1.5 months to 10 years (average: 4 ± 3 years). 17 patients had Erbñs palsy and 11 global plexus involvement. Eighteen had primary shoulder reanimation mainly via intraplexus neurotization. Palliative surgery in 25 patients included trapezius transfer for shoulder abduction, adductors release and rerouting of the latissimus dorsi and terres major for external rotation, scapula stabilization and rotational osteotomy of the humerus. The CT measurements included: humeral head retroversion, spinoscapular angle, glenoid fossa inclination, congruence of the humeral head to the glenoid and distance of the lower angle of the scapula from the midline. Results: Preoperatively the humeral head was subluxated or dislocated posteriorly and had decreased retroversion. The hypoplastic scapula had winging and increased distance from the midline, while the glenoid fossa was more retroverted. Postoperatively all the above measurements were improved. Conclusions: Novel measurements on CT scans of bilateral shoulders provide valuable information. Surgical intervention signiþcantly improves the functional anatomy and the dynamics of the shoulder joint.