Although obesity is a very common eating disorder, bulimia and anorexia also show an increasing tendency too among teenagers. Object of the study: to evaluate the knowledge of highschool students about eating disorders and to follow the efficacity of health education classes. We made a testpaper with easy questions about eating disorders which was followed by a health education class. After this students were asked to complete another testpaper with difficult questions. Some of them completed it after 10 days. Results: the knowlodge of students before the health education classes was 51%, and after the classes 85%. We did not find a significant difference regarding gender and provenience.