STUDY OBJECTIVES:To examine sleep duration and the association between insufficient sleep duration and life- style factors in a representative sample of Greek children and adolescents. METHODS:Population data derived from a school-based health survey carried out in spring 2015 on 177,091 children (51% male) aged 8 to 17 years (participation rate was approximately 40% of the total population). Dietary habits, sleeping hours (weekdays and weekend), physical activity status, and sedentary activities were assessed through electronic questionnaires completed at school with assistance of teachers. Anthropometric and physical fitness measurements were obtained by physical education teachers. RESULTS:A greater proportion of males than females (42.3% versus 37.3%, P < .001) and of children compared with adolescents (42.1% versus 32.8%, P < .001) reported insufficient sleep duration. Insufficient sleep duration was associated with unhealthy dietary habits such as skipping breakfast (odds ratio [OR] 1.30, 95% confidence interval [CI] 1.25-1.35), fast-food consumption (OR 1.35, 95% CI 1.29-1.41), and consuming sweets regularly (OR 1.32, 95% CI 1.25-1.39). Insufficient sleep duration was found to be associated with insufficient dietary habits (OR 0.59, 95% CI 0.54-0.64), increased screen time (OR 1.26, 95% CI 1.21-1.31), and being overweight/obese (OR 1.21, 95% CI 1.17-1.25), after adjusting for several covariates. CONCLUSIONS:Insufficient sleep duration was associated with an unhealthy lifestyle profile among children and adolescents in this study. Results support the development of interventions to help students improve sleep duration.