Described are the borderlines of the hypothalamus, its nuclei and fiber connections and its functions. The vascular supply of the hypothalamic area is included. Furthermore measurements of the IIIrd ventricle and distances between surface areas of the brain and skull as well as different landmarks near the hypothalamus are presented. For example the distance between the frontal pole and the lamina terminalis in our material measures 59.3 (52-65) mm. Distances for the different approaches to the hypophyseal region (transsphenoideal, pterional, supra- and infratentorial, transcallosal and transventricular) are also given.