Since the beginning of the 21st century, as intraoperative monitoring has been steadily spreading in Japan and globally, the values of motor-evoked potentials, visual-evoked potentials, and cortical-evoked potentials have been described. There are a wide variety of monitoring methods; the diseases handled are not limited to brain lesions, but extend also to spinal cord and spinal lesions; and there are many problems that have not yet been solved. Possible precautions are indicated by means of a video of an actual case site. Considerations are presented regarding the setting of this monitoring method, utilized in relatively frequent diseases and associated intraoperative judgments.