Objective: To investigate whether supplementing older men with vitamins B12, B6, and folic acid improves cognitive function. Methods: The investigators recruited 299 community-representative hypertensive men 75 years and older to a randomized, double-blind controlled clinical trial of folic acid, vitamin B6, and B12 supplementation vs placebo over 2 years. The primary outcome of interest was the change in the cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-cog). A secondary aim of the study was to determine if supplementation with vitamins decreased the risk of cognitive impairment and dementia over 8 years. Results: The groups were well-balanced for demographic and biochemical parameters. There was no difference in the ADAS-cog change from baseline to 24 months between the placebo (0.8, SD 4.0) and vitamins group (0.7, SD 3.4). The adjusted scores in the treatment groups did not differ over time (placebo 0.2 lower, z = 0.71, p = 0.478). There was a nonsignificant 28% decrease in the risk of cognitive impairment (odds ratio 0.72, 95% confidence interval 0.25-2.09) and dementia (hazard ratio 0.72, 95% confidence interval 0.29-1.78) over 8 years of follow-up. Conclusions: The daily supplementation of vitamins B12, B6, and folic acid does not benefit cognitive function in older men, nor does it reduce the risk of cognitive impairment or dementia. Classification of Evidence: This study provides Class I evidence that vitamin supplementation with daily doses of 400 μg of B12, 2 mg of folic acid, and 25 mg of B6 over 2 years does not improve cognitive function in hypertensive men aged 75 and older.