The aim of this study was to measure the prevalence of teenage vegetarianism and associated food habits and beliefs. Two thousand senior secondary school students (mean age 16 years), from 52 schools in South Australia, participated in a two part survey. The findings show that teenage vegetarianism is primarily a female phenomenon, ranging in prevalence, according to definition, from 8 to 37% of women and 1 to 12% of men. Support for vegetarian practices was high especially from mothers (63%) and classmates (46%). Generally, "teenage vegetarians" consumed fewer red meats than non-vegetarians but ate more chicken. They cited health, animal welfare and environmental reasons in support of their habits. The importance of operational definitions of vegetarianism is emphasized and the findings are discussed in relation to likely motivational influences.