Five patients are described with brachial plexus injuries complicating median sternotomy for cardiac surgery. The lower roots (medial cord) of the plexus were most affected and in some cases the lesions were bilateral. Pain was a prominent feature and although motor and sensory symptoms both occurred, motor signs were more prominent than objective sensory loss. Recovery was protracted and sometimes incomplete. Traction or compression of the plexus (or both) are the major possible mechanisms of injury; our experience and that of others suggests that traction is the more probable mechanism.