Twenty consecutive patients with spinal arteriovenous malformations (AVMs) were found to have either a progressive, remitting or remitting-progressive course of disease. A characteristic progressive neurological decline was observed in 11 patients with dural fistulas and a similar decline was seen in 5 of the 9 patients with intradural AVMs. In addition to paraparesis and mixed sensory disorder, which ascended to a level of about T10, areas with spared sensation were occasionally found below this level. All cases with this progressive longitudinal myelopathy showed radiological evidence of a dilated medullary venous plexus. All patients were treated by embolization with only a low frequency of complications. Follow-up data verified a significant improvement of motor and sensory function, mainly during the first year after embolization. Cases with progressive neurological decline (dural and intradural AVMs) stopped deteriorating or improved and cases with a history of acute incidents (intradural AVMs) probably run less risk of acute deterioration.