Early signs of spinal cord injury on neurologic examination have been the primary indication to proceed with myelography in patients with possible spinal epidural metastases. With this approach, loss of ambulation occurs in more than one half of the patients. In an attempt to diagnose epidural metastases before the onset of myelopathy, we designed a prospective study based on the development of back pain, a precursor of spinal cord injury in nearly all cancer patients. Eighty-seven patients were studied. A high incidence of epidural metastases was found in patients with myelopathy (78 percent). In addition, patients with radiculopathy alone frequently had epidural tumor (61 percent). In 36 percent of the patients who presented with back pain but who had normal neurologic findings, there was evidence of epidural metastases on myelography; all of those patients had vertebral metastases on plain roentgenogram. Over-all, the plain roentgenogram of the spine correctly predicted the presence or absence of epidural tumor in 83 percent of the patients. Whereas 93 percent of the patients with myelopathy had more than 75 percent myelographic block, this occurred in 53 percent of those with radiculopathy and in only 33 percent of those with back pain and normal neurologic findings. In most cancer patients, spinal epidural metastases are both detectable and significantly less extensive before the onset of spinal cord injury. © 1981.