To assess the consequence of the presence, grade, and asymmetry of carotid artery stenoses on the optic nerve sheath diameter (ONSD) measured by ultrasonography. ONSD was measured with B-mode ultrasonography in 129 patients referred for duplex and color Doppler imaging of the carotid arteries. Internal carotid artery stenosis was graded on the basis of peak systolic flow velocity. The mean ONSD was 3.04 ± 0.38 mm in the patients without or with <50% internal carotid artery stenosis and 2.46 ± 0.35 mm in those with >70% stenosis. There was an average difference of 0.58 mm between the ONSD of the patients with <50% and the patients with >70% stenosis. ONSD is lower in patients with carotid artery stenosis. Carotid arteries should be investigated, especially in patients with cardiovascular risk factors or diseases, before interpreting ONSD values.