Recent studies have shown that the prevalence of vegetarianism among the general population in western societies ranges between 2% and 9%. Information regarding the prevalence of vegetarianism among exercisers is lacking. The aim of the present pilot study was to determine the prevalence of vegetarianism among regular exercisers in Greek gyms, as well as assess their dietary habits, exercise habits, and attitudes toward health and environmental issues. 291 regular gym clients completed an anonymous descriptive online questionnaire containing 65 questions divided into five sections (demographic characteristics, dietary habits, physical activity, dietary supplements, environment). Thirty responders (10.3%) identified themselves as vegetarians, spanning the entire spectrum of vegetarianism, from raw vegan to semi-vegetarian. Compared to omnivores, vegetarians had lower body weight, were more concerned about their health and convinced about the health benefits of their dietary choices, were surrounded by more vegetarians socially, consumed fast food and ate out less often, used more dietary supplements, and were better informed about what a sustainable diet is (all p < 0.05). Vegetarians did not differ significantly from omnivores in demographic characteristics, alcohol consumption, smoking habits, prevalence of psychogenic eating disorders, or exercise practices (except for practicing more yoga/Pilates). In conclusion, we report, for the first time, a considerable prevalence of vegetarianism among regular exercisers in gyms. Our findings demonstrate important similarities and differences between exercising vegetarians and omnivores (partly at odds with those seen in the general population) and highlight nutritional and environmental issues on which both groups should be better educated.