Somatosensory evoked potential(SSEP) has been recorded during 31 operations for intracranial aneurysm. We had monitored the SSEP in each stage of aneurysm surgery(preoperative, anesthetic induction, dura opening, temporary vascular occlusion, aneurysm neck clipping and 30 minute after aneurysm neck clipping). Temporary occlusion of intracranial arteries have performed in 21 cases. In cortical amplitude of more than 50% as compared with induction was considered to be "significant" SSEP change. Eleven out of 21 cases of temporary vascular occlusion showed significant decrease of amplitude. Three out of 4 cases with flat wave had new neurologic deficits postoperatively. We studied the relationship between SSEP changes and postoperative neurologic deficit and concluded as follows: 1) The monitoring of amplitude of SSEP may help control the duration and number of application in temporary clipping during aneurysm surgery. 2) Decreased in amplitude with temporary clipping, especially flat wave, is a strong suggestion of the postoperative neurologic deficit. These results indicate that monitoring of SSEP during aneurysm surgery would be helpful to reduce the incidence of postoperative neurologic deficits.