We retrospectively studied 46 patients with symptomatic retinal artery occlusion and assessed the pattern and extent of carotid artery disease ipsilateral to the retinal artery occlusion. Ipsilateral internal carotid artery atherosclerotic lesions were virtually limited to the cervical arterial segment; 50% of such lesions were plaques or stenoses of less than or equal to 60%, whereas 15% of the angiograms were normal. No clinical features were significantly associated with a flow-limiting carotid stenosis of greater than 60%. Contrary to previous reports, the type of retinal artery occlusion, whether branch or central artery occlusion, was not predictive of severe underlying carotid stenosis or occlusion. Likely mechanisms of retinal artery occlusion include in situ thrombosis and emboli from carotid, and possibly cardiac, sources. Extension of thrombus from an occluded carotid artery into the ophthalmic artery did not appear to be a mechanism of retinal artery occlusion.