We present an extremely rare case of traumatic spinal cord herniation due to a brachial plexus avulsion injury and provide a review of the literature of spinal cord herniation. Spinal cord herniation is an uncommon condition that can occur spontaneously or as a result of surgery or trauma. This condition often presents with symptoms and signs as Brown-Séquard syndrome. Traumatic pseudomeningoceles after a brachial plexus avulsion injury have been reported. But transdural herniation of the spinal cord into this pseudomeningocele is an extremely rare and poorly documented condition. There is only two reports of this condition in a thoracic case. The authors report the case of a 22-year-old man presented with a 2-year history of quadriplegia. He was involved in a motorcycle accident, 3 years prior to his presentation. Four years after the initial right brachial plexus injury, he was not able to walk independently. Magnetic resonance imaging (MRI) and computerized tomography (CT) myelography revealed a lateral pseudomeningocele arising from the right C6-7 and C7-T1 intervetebral foramen and cervical spinal cord herniation into this pseudomeningocele. The patient underwent primary closure of pseudomeningocele to prevent spinal cord reherniation. He can walk with cane and use left arm unrestrictedly at the 2-year follow-up examination. Spinal cord herniation following traumatic nerve root avulsion is extremely rare but it should be considered in the differential diagnosis of patients presenting with delayed myelopathy or Brown-Séquard syndrome.