We studied the course and interrelationships of the different segments and loops of the intracranial internal carotid artery (ICA) by means of morphometric measurements and observation of the correlation between their microsurgical anatomy in cadavers and radiographic anatomy in normal computed tomography (CT) scans of adult patients. Twenty sphenoidal blocks from formalin-fixed cadavers were used for microanatomical dissection under the surgical microscope, and another 20 sphenoidal blocks were used to inject the ICAs with barium. Plain radiographs of these injected blocks were obtained in anterior-posterior, lateral, and horizontal planes, and morphometric analyses of the different loops of the ICA were done as well. A similar analysis was also done on normal CT scans of 20 adult patients after excluding any pathology that might affect the location, shape, or course of the ICAs. The distance between the 2 ICAs was greatest at the posterior loop and decreased gradually as the arteries proceeded forward through the lateral and medial loops, not changing significantly from the medial to the anterior loops. The distance between the 2 ICAs at the cavernous sinuses (the “intercavernous” distance) and the distance of the different loops from the midline were measured within the sphenoidal blocks, and these values were compared with similar measurements on the patients' CT scans. The venous channels that connect the cavernous sinuses were also dissected in formalin-fixed cadaver blocks, and the findings are discussed.