The intracranial internal carotid artery (ICA) is a muscular artery and lacks external elastic lamina (EEL). Stenosis of the intracranial ICA is relatively uncommon, but the most common site is the cavernous portion. The characteristics of the arterial wall structures were examined using serial 3-mm sections of 32 intracranial ICAs obtained from 50 cadavers to identify where the EEL disappeared. The portions of the ICA where the intima exhibited thickening were also determined. Both the internal elastic lamina (IEL) and EEL were observed in all 32 specimens of the petrous portion of the ICA. Only the IEL was observed in all 32 specimens of the intradural portion of the ICA. The EEL had disappeared in 31 of the 32 specimens of the horizontal segment of the cavernous portion of the ICA. Intimal thickening of the ICA was observed in 23 of 32 ICA specimens, and frequently appeared in the horizontal segment of the cavernous portion of the ICA. The EEL disappeared in the cavernous portion of the ICA, which is the most common site of stenosis of the intracranial ICA. Change in the elasticity of the arterial wall in the cavernous portion may be an important factor in the process of atherosclerosis in the intracranial ICA.