Residual limb shortening is common after obstetric brachial plexus palsy. The exact limb-length discrepancy remains undetermined, and the purpose of this paper is to determine the resultant discrepancy. Twenty-two skeletally immature patients with obstetric brachial plexus palsies were examined. Radiographs of both the involved and uninvolved humerii and forearms were obtained with a radiographic ruler placed adjacent to the extremity. Each limb segment was measured and the discrepancy calculated as a percentage compared with the normal side. Twenty-one of the 22 children had some shortening of the limb at both the humerus and forearm level. The involved limb averaged 92% of the uninvolved limb. The humeral length averaged 93% and the forearm length averaged 90%. Children with upper brachial plexus lesions had significantly less forearm and total limb shortening compared with those with global lesions. There was no correlation between age and percentage difference of the humeral, forearm, and total length.