Objective:(i) To examine demographic and health characteristics of women of reproductive age on a vegan diet in Australia and compare these to the general population; (ii) to identify sources and intake of vitamin B12 and compare intake to current recommendations and (iii) examine associations between participant characteristics and adequacy of vitamin B12 intake.Design:In this cross-sectional study, data were collected via an online survey. Demographic and health characteristics of women on a vegan diet were compared with women in the general population (using Australian Bureau of Statistics data). Intake of vitamin B12 was estimated using a FFQ and estimation of supplemental intake.Setting:Australia.Participants:Participants (n 1530) were women aged 18–44 years who had been on a vegan diet for at least 6 months.Results:While BMI, smoking habits and intakes of fruit and vegetables compared favourably with the general population, 26 % of respondents had estimated intakes of vitamin B12 below recommendations. Analyses of relationships between vitamin B12 intake and participant characteristics revealed that the strongest predictor of intake was supplementation (P < 0·001); however, 25 % had not supplemented with vitamin B12 in the past 3 months.Conclusions:The vitamin B12 intakes of a substantial proportion of Australian women of reproductive age consuming a vegan diet do not meet the recommended intake, which could adversely affect their health, and, if they are pregnant or lactating, that of their infants too. There is a need for further research in this area to identify effective strategies to address this situation.