METHODS This study was done to assess the pathophysiology of neurogenic intermittent claudication by measuring the epidural pressure at walking. OBJECTIVE Changes in epidural pressure during walking in patients with neurogenic intermittent claudication and in normal individuals were analyzed. BACKGROUND Neurogenic intermittent claudication may be caused by compression of the nerve roots or may be a result of nerve root ischemia. The exact pathogenesis of neurogenic intermittent claudication is uncertain. METHODS Local epidural pressure changes at the stenotic level during walking were analyzed in 12 patients with lumber spinal stenosis and seven normal individuals. a flexible pressure transducer was inserted into the epidural space and placed at the L4-L5 level. The epidural pressure was monitored continuously during walking. The pattern of the pressure change was assessed by gait analysis using a foot switch. RESULTS The pressure was changed during walking. The pressure had a wave pattern of increase and decrease, and this pattern was repeated during walking. Intermittent pressure increase was seen about 90 times per minute while walking at a velocity of 2 km/h. An increase in epidural pressure occurred at the double-supporting phase in each gait cycle. CONCLUSIONS The pressure was high in spinal stenosis and low in normal individuals. The increase of epidural pressure at simple walking was higher than walking with lumbar flexion. Intermittent compression to the nerve roots during walking may be a cause of neurogenic intermittent claudication.