In eleven years, 30 (3.2%) of 951 patients with spinal cord injury developed cervical syringomyelia. This condition was found in 22 (4.5%) of 488 posttraumatic tetraplegic and 8 (1.7%) of 463 posttraumatic paraplegic patients; the incidence was about 8 per cent in patients with complete tetraplegia. This study demonstrated the rarer clinical manifestations of syringomyelia, namely autonomic dysfunction, alterations in the sensory level with postural changes, the early occurrence of tendon areflexia and painless motor deterioration. Prolonged F wave latencies were present in all patients with a demonstrable syrinx and a higher protein content was found in the syrinx than in the cisternal fluid. Some of the symptoms and signs in a proportion of the patients treated conservatively remained stable without operative treatment over a number of years. Most of the patients in whom operation was performed for progressive motor weakness or severe pain had good postoperative results although a few developed late sensory or motor changes. There was no benefit in operating on a patient with a small syrinx.