The number of vegans in the world is growing and in Slovakia and the Czech Republic they make up 1% of the population. The vegan diet excludes all foods of animal origin and vegans are therefore potentially at risk of vitamin B12 deficiency. The aim of the study was therefore to determine, whether vegans supplement vitamin B12 and whether the doses used are sufficient. The research involved 1337 vegans from Slovakia and the Czech Republic, who completed electronic questionnaire in the Click4survey.com web application. Overall, 55.5% (742) of respondents supplemented vitamin B12 regularly and 32.54% (435) irregularly. Despite inconsistent recommendations for vitamin B12 intake, most vegans received a sufficient dose, averaging 371 µg with a median of 286 µg. Vitamin B12 was not supplemented by 11.97% (160) of participants and together with 17.35 % (232) respondents, who supplemented the inadequate dose, 29.32% (392) of respondents were at risk of vitamin B12 deficiency. By applying statistics on the incidence of vitamin B12 deficiency according to the regularity of supplementation from the work of Selinger et al. it was further estimated that 15.24% (204) of respondents currently suffered from vitamin B12 deficiency. Compared to the occurrence of a deficit in Slovak vegans in 2000, when it affected 78% of vegans, the results suggest a positive trend. . Nevertheless, vitamin B12 deficiency is a significant risk for vegans, especially for pregnant and lactating women and children.