The investigation deals with the topography of principal sulci and of the temporal lobe within the international 10-20 system for electrode placement. Using magnetic resonance imaging in 16 healthy volunteers, the location and variability were studied for the superior central sulcus, the sylvian fissure, the calcarine sulcus and the anterobasal temporal lobe. Variation zones for these structures within the reference system are described. Craniocerebral variability was most pronounced in the areas remote from the relatively constant central and lateral sylvian region.