Five patients with spinal dural arteriovenous (AV) fistulas who experienced acute or subacute onset of myelopathy in the absence of hemorrhage are described here. Therapeutic intervention, including anticoagulation, embolization, and surgical ablation of the dural AV fistula, stabilized or reversed neurological deterioration in these patients. Partial but significant recovery occurred in most patients. Our experience indicates that in the early stages of acute or subacute myelopathy caused by spinal dural AV fistulas the pathophysiology is venous congestion, not thrombosis. Therefore, in patients with spinal dural AV fistulas and rapidly progressive myelopathy (Foix-Alajouanine syndrome), the myelopathy is probably caused by deterioration of the compensatory capacity of the spinal cord to accommodate venous congestion (compensation/decompensation phenomenon). This departure from classical observations is important clinically in that early diagnosis and proper management of venous congestion are likely to result in a successful outcome.