The attitudes towards body weight and shape, desire for thinness and dieting behaviours were investigated in pre-adolescent and adolescent girls and boys (547 elementary school students, 615 junior high school students, and 470 senior high school students) aged 10-17 years in Osaka Prefecture, Japan, by a self-report questionnaire. Forty-eight per cent of 10-year-old females and 84% of 17-year-old females categorized themselves as 'fat' or 'too fat'. The fear of weight gain and desire for thinness was reported in 35% and 51% of 10-year-old girls, respectively, and increased progressively with ageing to 79% and 87% of 17-year-old girls. In contrast, these were reported by 20-30% of boys in the corresponding age groups. Some practices to be slim were found in 22% of the 10-year-old girls, and increased to 37% among the 17-year-old girls, whereas they were found in around 20% of the boys at each age. The practices to be slim were found in 32% of the girls who were 85-90% of the standard body weight (SBW) and in 14% of the girls less than 85% of the SBW. These results suggest that significant concerns about weight and shape and dieting behaviours are present in young Japanese girls and increase progressively with age. These results are compatible with those in Western society.