OBJECTIVE: To identify behavioural and social correlates of objectively-measured sedentary time in young people. DESIGN: Cross-sectional analysis of data from the European Youth Heart Study (EYHS). SETTING: Schools in Denmark, Estonia, Portugal and Norway. PARTICIPANTS: Invited using a two-stage cluster sampling procedure. Analyses include 2107 children (9-10 years) and adolescents (14-15 years). Assessment of independent variables: Seven behavioral and 15 social variables assessed by parental and computerized child questionnaires. MAIN OUTCOME MEASURE: Sedentary activity as assessed by accelerometry (10-minute blocks at