Sophisticated spectral analysis and mapping of the EEG with computer techniques provides objective and reliable diagnostic information, which is superior to that obtained by naked-eye observation, even by experienced clinicians. In our department, a topographic system was introduced as one of major adjuncts to EEG examination in 1980, and we devised our own software (dynamic topography, compound dynamic topography, deviation ratio topography) to facilitate its clinical application. Topographic mapping is applied to assessment of the dominant hemisphere, evaluation after medical and surgical treatment, spatial localization of epileptic foci, and intraoperative monitoring for cerebral hypoperfusion. Besides these surgical applications, topographic analysis has contributed to human neurophysiology, for instance in determining the participation of the dentatethalamic tract in movement-related cortical potentials. Our experience of the neurosurgical and neurophysiological applications of topographic mapping will be presented.