A young male Indian Rhesus macaque infant presented to a national primate research center treatment clinic when he was noted to be dragging his left forelimb while clinging to his mother in the colony. On physical exam, he had no sensory or motor function in his proximal or distal left forelimb. The forearm had decreased tone with mild muscle atrophy in all muscle groups. All other physical exam findings were within normal limits. Radiographs revealed no evidence of a fracture. A complete brachial plexus lesion was presumptively diagnosed. To further characterize the extent of the injury, a nerve conduction study (NCS) and electromyography (EMG) was performed. Electrical stimulation to the median and ulnar nerves did not result in appropriate action potentials. In addition, multiple muscles of the left forelimb (biceps brachii, triceps brachii, abductor pollicis brevis, flexor carpi ulnaris, common digital extensor, and infraspinatus) were found to lack normal electrical impulses suggesting complete nerve damage to left spinal nerves C-5 to T-1. The decision was made to amputate the limb at the scapulohumeral joint.