Hyperhomocysteinemia is a strong risk factor for atherosclerotic vascular disease, and elevated serum homocysteine is correlated with vitamin B deficiency. In this pilot study, significantly elevated homocysteine levels were found in patients with Alzheimer's disease as well as in patients with vascular dementia, probably indicating similar pathophysiological pathways. We found significant correlations between low folic acid concentrations as well as high homocysteine concentrations and cognitive decline. Supplementation with folic acid may be an inexpensive way to reduce elevated homocysteine levels in demented patients.