In the interhemispheric approach (IHA) for the distal anterior cerebral artery (DACA) aneurysms, the surgical trajectory to a DACA aneurysm is very important because surgeons sometimes encounter the intraoperative disorientation and the premature rupture. The purpose of this study was to clarify the anatomical landmarks indicating the trajectory to the genu of the corpus callosum (GCC) at the early stage of dissection for the correct intraoperative orientation. “Point A” was defined as the crossing point between the frontal bone and the line connecting the projected external acoustic opening (EAO) and the GCC on the midline slice of the sagittal three-dimensional computed tomography angiography (3D-CTA) images. We measured the distance from the nasion to Point A using midline sagittal slice images from 50 patients who underwent 3D-CTA at our institution. The average distance was 7.0 cm (±0.3 cm). Therefore, the direction of the spatula inserted in the direction of the EAO from Point A (7 cm above the nasion) corresponds to the trajectory to the GCC. In DACA aneurysms of the A3 segment, the pericallosal artery distal to the aneurysm can be safely identified by dissecting the interhemispheric fissure distal to the trajectory to the GCC. In DACA aneurysms of the A4 or A5 segment, the parent artery of the aneurysm can be safely identified by dissection along the trajectory to the GCC. Point A and the EAO can be used as landmarks indicating the trajectory to the GCC for the correct intraoperative orientation in the IHA for DACA aneurysms.