Eight cases of spinal sarcoma complicating Paget's disease seen in different centers were reviewed. Clinical and radiological features of this condition were determined on the basis of these 8 cases and of 51 previously published cases. In the current series as well as in previous reports, most cases involved the lumbar and sacral spine and manifested as low back pain with sciatica and early development of neurological deficits. Roentgenographic diagnosis proved difficult because of the anatomic complexity of the spine and architectural changes characteristic of the pagetic bone. The most common radiological features was a mixed pattern with both sclerosis and central osteolysis. Computed tomography performed in one patient of current series disclosed osteolysis of the sacrum (not visible on plain roentgenograms) with tumor spread to adjacent soft tissues. Features shared by spinal and nonspinal sarcomas complicating Paget's disease include advanced mean age of patients, predominance of osteogenic sarcomas among histologic forms, increased risk of sarcoma in polyostotic Paget's disease, and a very grim prognosis. Development of a neurological deficit in a patient with Paget's disease is an unusual occurrence which should suggest sarcomatous transformation. Roentgenographic changes are difficult to identify on plain films of the spine and consequently CT scan studies are warranted whenever a sarcoma is suspected.