Plant-based diets are associated with numerous health benefits but also bear risks of micronutrient deficiencies if inadequately planned. The risk of nutrient deficiencies can be reliably reduced by supplementation but requires risk-awareness. We distributed a paper-and-pencil questionnaire to n = 902 healthcare professionals attending a congress on plant-based nutrition (VegMed 2018, Berlin). On the day of the survey (21 April 2018), n = 475 questionnaires were returned and analyzed descriptively. Of the n = 213 strict vegan participants, 2% (n = 5) took no supplements at all. All supplementing vegans reported taking vitamin B12. Almost three-quarters of vegans (73%, n = 152) took vitamin D, and 22% (n = 45) reported taking omega-3 fatty acids. Iron was supplemented by 13% (n = 28), iodine by 12% (n = 25), calcium by 11% (n = 22), zinc by 7% (n = 14), magnesium by 5% (n = 11), and selenium by 4% (n = 9). For 11%, a supplement other than vitamin B12 was subjectively most important. Nearly 50% had their vitamin B12 levels laboratory tested at least once a year; nearly one-quarter reported testing every two years, and another one-quarter rarely or never. Participants following a vegan diet were better informed about institutional recommendations of the German Nutrition Society and the Academy of Nutrition and Dietetics for vegan diets than participants following vegetarian or omnivorous diets. Vegan nutrition in pregnancy/lactation period and childhood was considered most appropriate by vegans. Despite a high awareness of potential health risks associated with vitamin B12 deficiency on a strict vegan diet and a comprehensive understanding of the official dietary recommendations of nutrition societies, use of supplements and performance of regular laboratory tests were only moderate among vegan healthcare professionals. Considering the paramount importance of adequate supplementation of critical nutrients to avoid nutrient deficiencies, scientific and public discourse should be further facilitated. Further investigation of the supplementation behavior of vegan health professionals could be of particular interest, as a possible correlation with the quality of their own nutrition counseling is not inconceivable.