Limited physical activity (PA), sedentariness and unhealthy eating increase the risk of non-communicable diseases and conditions that are leading causes of mortality, disability pensioning, extended use of social benefits, years lived with disability, and reduced quality of life. Physical inactivity and unhealthy eating habits thus represent important preventable causes of life years lost1 and years living with disability, implying unnecessary high costs to society. The overarching aim of the project is to ascertain causes of PA, inactivity and unhealthy eating behavior in the transition from childhood to adolescence, a critical phase for passing on healthy PA- and eating habits from early to later ages and thus a crucial periode for promotion of good health and quality of life. We will take the advantage of our on-going, prospective study (The Trondheim Early Secure Study - TESS, n=997) of a representative community sample of children, who have been intensively and repeatedly studied from age 4 to 14, aiming to re-study these participants when 16 and 18 years of age. The ALSPAC data will be used to compare and replicate findings.