We have reviewed 21 cases with the clinical diagnosis of Post Traumatic Syringomyelia (P.T.S.). Fifteen of these cases had proven syrinx formation on Contrast Computed Tomography (C.C.T.) and the other 6 had obviously abnormal cords. A much earlier onset of P.T.C.M. was found in complete spinal injuries than in incomplete ones. We have discussed the technique of contrast computed tomography used at this hospital, its value in the diagnosis of this condition and its ability to define actual spinal cord structure. Most cases (91%) benefitted from surgery and several had marked sensory improvement, which previously has been described as unusual. Syringo-cisternal shunting, a new technique for the drainage of cervical and upper thoracic syrinxes is described. A theory is proposed to explain why, in some patients with classical presentations of P.T.S., no syrinx was found on C.C.T., although abnormal cords were found in all cases. It is felt that these abnormal areas of spinal cord are responsible for the presenting symptomatology and may be precursors of syrinxes.