<b><i>Background/Aims:</i></b> Alzheimer's disease (AD) is an irreversible neurodegenerative disorder and is the commonest form of dementia. One aim of this study was to determine whether AD individuals have altered plasma folate, vitamin B₁₂ and homocysteine (Hcy) levels compared to controls. The other aim was to investigate correlations between B vitamins and buccal biomarkers to test whether they are influenced by B vitamin status. <b><i>Methods:</i></b> Folate, vitamin B₁₂ and Hcy were measured using ARCHITECT® and AxSYM® assays. Genomic stability was measured using the buccal micronucleus cytome assay. <b><i>Results:</i></b> The area under the receiver operating characteristic curve for AD basal cells was 0.96 (p < 0.0001), for karyorrhectic cells 0.88 (p < 0.0001) and for basal and karyorrhectic cells 0.91 (p < 0.0001). Hcy was significantly increased (p = 0.0003) compared to controls. Plasma vitamin B₁₂ in controls showed a positive correlation with pyknosis (r = 0.5365, p = 0.004), karyolysis (r = 0.5447, p = 0.004) and condensed chromatin (r = 0.5238, p = 0.006). Plasma vitamin B₁₂ in AD cases showed a positive correlation with micronuclei (r = 0.3552, p = 0.04) and basal cells (r = 0.3448, p = 0.04), whilst plasma Hcy showed a negative correlation with karyorrhectic cells (r = -0.4107, p = 0.01). <b><i>Conclusions:</i></b> Hcy was significantly increased in AD cases relative to controls. The lower frequency of basal cells and karyorrhectic cells observed in AD cases may be explained by lower vitamin B₁₂ and higher Hcy levels, respectively.