A three-year-old boy is reported who had congenital spastic paraparesis caused by severe segmental narrowing of the spinal cord. X-rays of the spine showed thoracolumbar scoliosis and anomalies of the thoracic vertebrae from T5 to T11. Myelography, with CT scanning, demonstrated severe narrowing of the T5 to T12 segments of the spinal cord, measuring only 1.5 mm at T10. This is believed to be the first report of this unusual anatomical finding in congenital spastic paraparesis. An early embryonic vascular insult is thought to be the most likely cause.