Diastematomyelia is an uncommon dysraphic lesion of the spine which has been diagnosed more frequently since the advent of newer diagnostic methods. A series of 21 cases was examined using metrizamide myelography and computed tomographic metrizamide myelography (CTMM) over a 3-year period. These examinations, in addition to plain radiographs of the spine, have demonstrated certain features of diastematomyelia hitherto unreported. A bony or cartilaginous spur was an uncommon finding, occurring in only six cases. Also, the split spinal cord was found within an unsplit dural sac in 15 cases. Coexistent tethering of the spinal cord, even in the absence of a spur, was present in 16 of the 21 cases. CTMM proved superior to metrizamide myelography in demonstrating the spinal cord anomalies; plain films and CT are complementary in showing the bony anomalies. The radiographic investigative protocol of diastematomyelia includes plain anteroposterior and lateral spine films, metrizamide myelography, and CTMM. Conventional tomography and plain CT are unnecessary; improved density resolution and availability of computed radiographic anteroposterior and lateral scout views will further reduce the need for plain films and intrathecal injection of contrast medium.