By analyzing the surface configurations of the telencephalon of the bottlenose dolphin and four other cetacean species, we have been able to delineate the major sulcal and gyral patterns, define the basic lobular organization of the highly gyrencephalic cetacean brain and describe the general organization of the brain surface into major cortical territories. Although the cetacean endbrain presents many general mammalian features, the surface configurations of the brains of these aquatic mammals differ in many significant details from the patterns of other mammals. These departures are subtle in the rhinencephalic (median) zone of the telencephalon, are more prominent in the limbic (paramedian) zone and become outspoken in the dorso-lateral and posterior zones of the fundus of the hemispheres. The latter zones of the fundus display the widest interspecies variability as well as the most marked individual intraspecies variability among Cetacea. The more salient general features we have observed are: 1. (1) pronounced antero-posterior foreshortening of the forebrain with enhanced dorsal proplasia of the parietal lobes, blunting of the occipital lobes, and ventro-lateral proplasia of the temporal lobes; 2. (2) great transverse width of the dorso-lateral and posterior (epihippocampal) parts of the hemispheres and reduced width of the antero-ventral (epistriatal) parts; 3. (3) conspicuously small hippocampus contrasting with the great mass of the epihippocampal parts of the hemispheres; 4. (4) large olfactory lobes and massive septal area contrasting with small orbital lobes and striatum; 5. (5) relatively large insula, buried under a massive operculum, the latter disposed as a discrete lobule demarcated from the dorso-lateral wall of the hemisphere by a deep arcuate fissure; 6. (6) presence of a paralimbic lobe, unique in Cetacea, intercalated on the medial wall of the hemisphere between limbic and supralimbic lobes and covered by a special heterotypical cortex of the sensorimotor type—agranular motor anteriorly, granular somesthetic dorsally, and modified koniogranulose visual posteriorly; 7. (7) some degree of cytoarchitectonic homogeneity though areal differences can be resolved and some apparent homogeneity may be due to the gradual transition of one area into the other which is characteristic of the cetacean cortical areas; and 8. (8) unusual organization of the homotypical cortex of “associational” type. However, a resolution of this latter must wait thorough architectonic evaluation of the entire supralimbic lobe. The surface demarcation of the rhinencephalon and the cleavage of each hemisphere into concentric tiers (limbic, paralimbic and supralimbic) are sharper and clearer in the cetacean brain than in any other mammalian brain. The segregation of the special heterotypical cortices in the paralimbic lobe, cleaved from the medial hemispheric wall by arcuate longitudinal clefts, is, as far as we have been able to determine, unique for Cetacea. In contrast to primates, in which the somatic sensorimotor and special sensory cortices are widely separated by broad expanses of homotypical cortex (association cortex), these intimately thalamus-bound special heterotypical cortical areas in Cetacea remain largely on the dorsomedial wall of the hemisphere bordering on the epihippocampal limbus, and do not appear to extend onto the supralimbic fundus of the hemisphere. This uniquely cetacean feature characterizes one of the most interesting aspects of the evolution of the brain in these totally aquatic mammals.