244 Australian schoolchildren aged between 8 and 12 years indicated their current and ideal body sizes by means of Collins' pictorial figures. Children's height and weight were also measured. Body-mass indices were calculated from these data, and percentile ranks estimated according to international reference data. Consistent with Collins' findings, 39% of girls and 26% of boys wanted to be thinner than they perceived themselves to be; however, this desire was strongly related to actual body size so the percentages were very different for weight categories established on the basis of Body Mass Index. In the overweight quartile, 76% of girls and 56% of boys wanted to be thinner, whereas in the underweight quartile only 10% of girls and no boys wanted to be thinner. The response of overweight children may be sensible, but the desire of some underweight girls to be even thinner is of concern. Some recent literature suggests that underweight individuals tend to overestimate their body sizes. About a half of our underweight children slightly overestimated their body sizes but only one child overestimated grossly.