Background/Aims: The impact of vitamin B status on cognitive functioning in Alzheimer’s disease (AD) is disputed. Using a population-based sample, we examined the associations of vitamin B₁₂ and folate with cognitive functioning in clinical (n = 44) and preclinical (n = 39) AD. Methods: The groups were subdivided in terms of low (<200 pmol/l) versus normal levels of B₁₂ and low (<13 nmol/l) versus normal folate levels. Participants were administered tests of verbal and nonverbal episodic memory, visuospatial abilities and verbal fluency. Results: As expected, the preclinical AD group performed better than the AD group across most cognitive tests. More interestingly, the effects of low vitamin B₁₂ and folate levels were negligible across all cognitive tests in clinical and preclinical AD. Conclusion: These findings suggest that the influence of vitamin B deficiency on cognitive functioning is overshadowed by the neurodegenerative processes associated with AD.