Posttraumatic progressive myelopathy (PTPM) was studied in nine patients and grouped into three categories on the basis of characteristic radiographic findings and response to therapy: (a) myelomalacia with no cystic degeneration, which has poor response to therapy; (b) small cysts, with poor response to therapy; and (c) large cysts, which are effectively treated by decompression. One type dominated in each patient, although a mixture of types was present in each. Magnetic resonance (MR) imaging gave slightly improved resolution and specificity of type, decreased morbidity, and simplification of procedure in comparison with imaging by delayed computed tomographic metrizamide myelography (DCTM). DCTM and MR imaging results correlated nearly equally with those of intraoperative sonography (IOS) and pathologic study at surgery. IOS was superior to DCTM or MR imaging in detecting septations and small additional cysts. IOS also was helpful in myelotomy positioning, shunt placement, and verification of cyst decompression. MR imaging may replace DCTM in the preoperative evaluation of PTPM, followed by IOS imaging as indicated. Patients with nonmyelopathic signs and symptoms (e.g., radiculopathy) probably still require study with conventional and/or CT myelography.