Navigation skills deteriorate with age, but the mechanisms of the decline are poorly understood. Part of the decrement may be due to age-related vascular risk factors. The T allele in a C677T variant in methylenetetrahydrofolate reductase (MTHFR) gene is associated with elevated plasma homocysteine, which is detrimental to vascular integrity and has been linked to cognitive decline. We inquired if a combination of physiological (hypertension) and genetic (MTHFR 677T) vascular risks has a synergistic negative impact on cognitive performance in otherwise healthy adults. We tested 160 participants (18-80 years old) on a virtual water maze. Advanced age, female sex, and hypertension were associated with poorer performance. However, hypertensive carriers of the T allele performed significantly worse than the rest of the participants at all ages. These findings indicate that hypertension combined with a genetic vascular risk factor may significantly increase risk for cognitive impairment.