Five patients suffering from Erb-Duchenne brachial plexus birth palsy were prospectively studied with MRI. A group of 11 healthy children was used as a control to understand the MRI anatomy of the normal growing glenohumeral joint. A hypoplastic and flattened posterior part of the glenoid fossa and a blunt posterior labrum were found in all patients. Four patients had a blunt anterior labrum and a flattened humeral head. Three patients presented with a posterior subluxation of the humeral head. These results suggest that MRI provides a non-ionising and non-invasive method of demonstrating the early abnormalities of the shoulder associated with obstetrical brachial plexus paralysis, which may prompt orthopaedic correction.