We report a case of thrombotic occlusion of the left common iliac artery during an L5-S1 anterior interbody fusion exposed via a retroperitoneal approach. The loss of distal blood flow was detected by loss of cortical and peripheral somatosensory evoked potentials on the left lower extremity. Restoration of the blood flow resulted in gradual return of evoked potentials of the involved extremity. The neurophysiological and pulse oximetry monitoring of the lower extremities are extremely sensitive for an early detection of thrombotic occlusions and vascular complications.