Background and Aims: Total plasma homocysteine (tHcy) has been suggested as a risk factor of dementia. Our aim was to investigate potential differences in tHcy status in relation to the prescription of vitamin B12 and dementia diagnosis. We examined whether vitamin B12 prescriptions, a family history of dementia, or the need for home care service might be associated with tHcy values. Methods: A cross-sectional monocenter study comprising 926 consecutive subjects attending our Memory Care Unit was conducted. Results: Demented subjects being prescribed vitamin B12 had higher serum vitamin B12 (p = 0.025) but also higher tHcy (p < 0.001) and serum methylmalonate (p = 0.032), and lower serum folate (p < 0.001) than those who did not receive vitamin B12 prescriptions. tHcy levels were significantly higher in non-demented subjects receiving home care service (p = 0.007). This group also had lower serum albumin (dementia: p < 0.001; non-dementia: p = 0.004). There was no difference in renal function (estimated glomerular filtration rate) in demented or non-demented subjects with or without vitamin B12 prescriptions (dementia with/without vitamin B12 prescription: p = 0.561; non-dementia with/without vitamin B12 prescription: p = 0.710). Conclusion: Despite vitamin B12 prescriptions, demented subjects had higher tHcy and methylmalonate values. The elevated metabolite values could not be explained by differences in renal function. Thus, elderly subjects on vitamin B12 prescription appear to have unmet nutritional needs.