Computed tomographic (CT) myelography, when used with metrizamide, permits a reliable demonstration of syringohydromyelic cavities in the cervical spinal cord. We report 6 cases of cervical syrinx demonstrated by high-resolution CT 4 h after metrizamide myelography: these cavities, which were not suspected clinically, extended into the thoracic cord. In addition 4 cases were associated with Chiari Type 1 malformation and 1 case was associated with both Chiari Type 1 malformation and infratentorial arachnoid cyst. We recommend that CT evaluation of cervical syringohydromyelia routinely include the thoracic spine, in order to demonstrate possible thoracic extension of the cavity. Scans of the foramen magnum are also recommended, because of the possibility of concomitant lesions, especially Chiari Type I malformation.