Despite research documenting the body image concerns of adolescent females, and the association with eating disorders, less is known about children’s perceptions of body shape or the developmental roots of adolescent concerns. This study, involving 140 children aged 5-11, explored what children think is the ideal shape for an adult male and female and whether body shape is related to masculinity and femininity. Children saw a range of figures from very thin to very fat and were asked which they thought was ‘the nicest shape for a lady (or man) to be’. Girls and boys agreed about what is the ideal male shape, but differed in their perception of the ideal female shape from as early as 5 years old. Girls selected an ideal female figure that was significantly thinner than that chosen by boys, and the girls also aspired to a thinner figure for themselves. Girls as young as 9 years, though not overweight, admitted they were dieting. Also, 61% of 11-year-old girls said their mothers dieted compared with only 12% of boys. Significantly more stereotypically feminine traits were associated with a thinner female figure than with a fatter one, whilst masculine traits were not associated with any particular male somatotype. The findings suggest that to be feminine, a female has to be thin although males can be either thin or fat and still be considered masculine. The implications in terms of the distorted beliefs underlying eating disorders are discussed.