We examined sex and ethnic differences in central fatness, as assessed by waist circumference measurements, in 13 590 Millennium Cohort Study 5-year-olds. Measurements were expressed as z-scores based on reference data from the British Standards Institute. The cohort, especially girls, had larger waist circumference measurements than the reference population. Black children had larger waist, and children from other minority ethnic groups had smaller waist than White children. Girls, and Black children, in the United Kingdom are at particular risk for central fatness. Further research is needed to clarify ethnic and other influences on fat distribution, and the health outcomes associated with central fatness.