The aims of this paper are (a) to investigate how adolescents perceive and represent the body form with respect to being fat or thin, and (b) to describe the process of how they constructed the social representations for these latter two body conditions. The data were collected by means of individual and focus group interviews with adolescent female students in Brazil who were from 11 to 21 years of age. When the adolescents were questioned about their bodies, they talked about "being fat" or "being thin", even though they were not asked about weight issues. Following their own logic, they did not portray "feeling fat" and "feeling thin" as related to their "real" body condition or weight. Furthermore, in the adolescents' discourse, the concept of "normal weight" was virtually non-existent and was characterised as "nothing" or "more or less". By the end of the interviews, their depictions of these conditions of body weight included links from the body to their social relationships in the form of perceived group exclusion or inclusion. In our discussion we describe the adolescents' collective discourses on being fat or thin as integrated social representations, which incorporate both the physical and interpersonal dimensions of their experiences. We conclude by examining the practical implications of our findings for female adolescent behaviour, especially with respect to obsessive dieting and possible eating disorders. Finally we explore the possibility of educational programs to counter the media and other influences which give rise to the negative aspects of social representations of the body by adolescents. (Contains 4 tables and 6 figures.)