The infrequency of spinal cord infarction and paraplegia after occlusion of the descending thoracic aorta has effectively precluded statistical identification of risk factors. Reversible spinal cord ischemia (SCI), however, is more common, can be detected by intraoperative neurophysiologic monitoring, and can lead to irreversible spinal cord damage. Spinal somatosensory evoked potentials (SEPs) were monitored intraoperatively in 38 patients (18 days to 18 years) undergoing coarctation repair (1982-1986). Although no patients sustained perioperative neurologic dysfunction, 10 of 38 (26%) patients developed reversible SCI, as reflected by greater than 75% loss of SEP N1-P1 interpeak amplitude during aortic occlusion (mean clamp time, 29.1 +/- 1.1 min). During occlusion, seven of 38 (18%) sustained complete loss of the SEP; uniform and prompt (1 to 6 min after clamp release) recovery of the signal occurred in these patients with reperfusion following completion of the repair (n = 6), or temporary institution of partial occlusion (n = 1). By multiple regression analysis the degree of SCI was negatively related to the distal aortic pressure (mean 32.4 +/- 2.4 mm Hg, p = .03), and the occlusion PCO2 (mean 33.1 +/- 1.1 mm Hg; p = .013), and positively related to the change in proximal systolic pressure with aortic occlusion (mean 19.8 +/- 3 mm Hg, p = .003). We conclude that: (1) distal hypotension and SCI commonly occur during aortic occlusion for coarctation repair, and (2) intraoperative interventions that can potentially influence distal aortic perfusion and/or PCO2 should be used judiciously.