BACKGROUND Whether vitamin B12 deficiency is associated with cognitive impairment remains controversial. OBJECTIVE To determine the association between vitamin B12 serum levels and cognitive performance. METHODS Two-hundred and forty-one adults aged ≥ 60 years who had serum vitamin B12 serum levels measurement were included. Physical and cognitive evaluation was carried out, and three groups were formed: normal cognition (NC), mild cognitive impairment (MCI) and dementia. Vitamin B12 levels were classified as sufficiency (> 400 pg/mL), subclinical deficiency (201-400 pg/mL), and absolute deficiency (≤ 200 pg/mL). Multivariate linear regression analysis was used to evaluate the association between cognitive function and vitamin B12 levels after controlling for confounding variables. RESULTS Mean age was 81.4 ± 8.0 years; 68% were females; 17.8 % and 39.8% had absolute and subclinical vitamin B12 deficiency, respectively; 80 individuals (33%) met the criteria for MCI, and 70 (29%), for dementia. Those with MCI and dementia had lower vitamin B12 levels in comparison with those with NC after adjusting for age, gender and educational level (p = 0.019). CONCLUSIONS A statistically significant association was observed between global cognitive performance and levels of vitamin B12.