Objective:Sleep duration has been related to overweight in children, but determinants of sleep duration are unclear. The aims were to investigate the association between sleep duration and childhood overweight adjusted for family characteristics and unhealthy behaviours, to explore determinants of sleep duration and to determine with sleep competing activities.Method:A cross-sectional study was carried out in 2006 among 4072 children aged 4–13 years in the city of Zwolle, The Netherlands. In these children, data were available on measured height, weight and waist circumference, and from a parental questionnaire, on socio-demographic characteristics, child’s sleep duration, nutrition, physical activity and sedentary behaviour. Associations were studied in 2011 using logistic and linear regression analyses, adjusted for potential confounders.Results:Short sleep duration was associated with overweight for 4–8-year-old boys (odds ratio (OR):3.10; 95% confidence interval (CI):1.15–8.40), 9–13-year-old boys (OR:4.96; 95% CI:1.35–18.16) and 9–13-year-old girls (OR:4.86; 95% CI:1.59–14.88). Among 4–8-year-old girls no statistically significant association was found. Determinants for short sleep duration were viewing television during a meal, permission to have candy without asking, not being active with their caregiver and a late bedtime. For all children, short sleep duration was strongly associated with more television viewing and computer use.Conclusions:Association between sleep duration and overweight is not explained by socio-demographic variables, drinking sugared drinks and eating snacks. Parents have a key role in stimulating optimal sleep duration. Improving parenting skills and knowledge to offer children more structure, and possibly with that, increase sleeping hours, may be promising in prevention of overweight. © 2010 Macmillan Publishers Limited.