Evidence is mounting in support of a role for short sleep duration in increasing the risk of obesity in children(1–3). For the present study it was hypothesised that sleep duration would be negatively correlated with obesity. Participants were 261 children (46% male) aged 7–11 years attending three primary schools in Middlesbrough, UK. Anthropometric measurements were taken at school, and parental questionnaires provided background information and details of the children's bed, sleep and wake times on weekdays and weekend days. Sleep duration was estimated using the equation: ((sleep on week night×5)+(sleep on weekend night×2))/7. ANOVA was used to assess the relationships between sleep duration and obesity variables, controlling for the effects of age, gender, ethnicity and socio-economic status.