In a recent case-control study of 164 patients with clinically diagnosed Alzheimer's disease (AD), including 76 patients with the AD diagnosis confirmed postmortem, mean total serum homocysteine concentration was found to be significantly higher than that of a control group of elderly individuals with no evidence of cognitive impairment. Because homocysteine is considered an independent risk factor for vascular disease, this finding is consistent with the emerging hypothesis that vascular disease is a contributing factor in the pathogenesis of AD.