Purpose: Elevated plasma total homocysteine(Hcy) concentrations are associated with Alzheimer’s disease(AD) and vascular dementia(VaD). The purpose of this study is to examine the association of dementia with blood levels of Hcy, and its biological determinants folate and vitamin B12.Methods: The studied groups of 28 cerebro vascular disease(CVD) patients, 22 VaD patients, 51 AD patients, 20 mild cognitive impairment (MCI) and 25 healthy elderly subjects. These patients and control subjects were studied for Hcy, vitamin B12, and folate.Results: All patients and control subjects were compared for age, sex, educational level, and Hcy, folate and Vit.B12 levels. Hcy was significantly increased in VaD patients (mean ±.SD= 17.8±5.5 μmol/L) and AD patients (mean ±.SD=14.2±3.1 μmol/L. p<0.001) as compared to controls (mean ±.SD=9.9±2.1 μmol/L); AD patients also showed increased levels of Hcy. Folate levels were significantly reduced in both VaD (mean ±.SD=8.8±2.9 ng/ml) and AD (mean ±.SD=9.7±3.1 ng/ml; p<0.001) patients, vitamin B12 showed significantly reduced levels in VaD (mean ±.SD=230.53±22.1 pg/ml) and AD patients (mean ±.SD=285.92±22.8 pg/m). No significant relationship was observed between MCI and control subjects for folate, vitamin B12,and Hcy levels.Conclusion: Further large-scale prospective trials are required to assess whether lowering plasma Hcy levels prevent AD or delay progression of clinical symptoms of AD.