This study assessed the percent body fatness of British secondary school children and examined any variation in fatness according to school year, gender and ethnicity. 782 children aged 11 to 14 participated in the study. Body fatness was assessed using skinfold measures and obesity was classified using child-specific cut-off points. Results from 2 x 3 x 3 ways ANOVA indicated that approximately 25 to 30 percent of children were classified as obese. Significant differences were evident in body fatness according to gender (p less than 0.01) and ethnicity (p less than 0.01). Boys were leaner than girls and black children were leaner than white and Asian children (both p less than 0.01). Furthermore a significant gender x ethnicity interaction (p less than 0.01) was found. Both white and black boys had significantly lower percent body fat compared to white and black girls but Asian boys had similar percent body fat to Asian girls. The body fatness of British secondary school children may therefore be a cause for concern. (Contains 1 figure and 3 tables.)