Complex regional pain syndrome type I of vascular origin is difficult to detect unless the classic symptoms and signs exist and/or overt extremity trauma has precipitated the pain. The diagnosis is confirmed by relief of pain following a sympathetic nerve blockade. A 36-year-old woman with arterial occlusive disease of the right lower extremity presented with burning pain and hyperesthesia after sprain had occurred which was accompanied by motor weakness of right ankle. A lumbar sympathetic ganglion blockade with 2% lidocaine 10 ml and triamcinolone 80 mg produced prompt improvement of the pain and motion.