Two infants, younger than 2 months of age, had brachial plexus involvement and true paralysis secondary to osteomyelitis of the proximal humerus. To date, no previous cases of this association have been reported. Electromyography (EMG) demonstrated significant denervation in muscles innervated by the upper trunk, with scattered involvement of other muscles. Nerve conduction velocities were normal in both patients. Both patients had significant residual weakness after appropriate antibiotic therapy. One patient, 12 months after therapy for osteomyelitis, continued to demonstrate both clinical and EMG evidence of a lower motor neuron neuropathy. The pathophysiologic cause was thought to be ischemic nerve damage secondary to occlusion of vasa nervorum.