The rise in numbers of overweight/obese children in the UK is causing widespread concern. Biomedical constructions of body acceptability and 'good health' mean that overweight/obese young people are frequently seen as deviant. The socio-cultural contexts within which young teenagers become fat, and lay conceptualisations of fatness, have largely been ignored. This qualitative study involved in-depth interviews with teenagers aged 13-14 years (n = 36), drawn from families living in areas classified as socio-economically disadvantaged. Half of the sample had a Body Mass Index (BMI) classifying them as overweight or obese, whilst the remainder were classified as being 'normal' weight. Participants' embodied perceptions of fatness were complex and sometimes contradictory. We discuss what young teenagers perceive the influences on fatness and body size to be; the professed consequences of being fat; participants' experiences of attempting to lose weight; and, their reported interactions with friends and family relating to fatness and dieting. Participants rarely mentioned any health-related consequences of their own and others' fatness, although wearing 'nice' clothes and being slowed down were raised as considerations by girls and boys, respectively. 'Normal' weight teenagers who disliked their bodies or who wanted to lose weight often claimed to be anxious about this. Being very obese also led to anxiety and reported attempts at 'crash dieting'. Acceptance of body size/shape was, however, common amongst the overweight and obese teenagers, although some had attempted weight loss. The teenagers in this study were rarely supportive of friends or family who attempted to lose weight and frequently disagreed with others' perceptions of fatness. These findings are important as they contradict the common perception that being overweight/obese is related to body dissatisfaction and that young people have a fear of fatness.