Background Higher prevalence rates of unhealthy behaviours among lower socioeconomic groups contribute substantially to socioeconomic inequalities in health in adults. Preventing the development of these inequalities in unhealthy behaviours early in life is an important strategy to tackle socioeconomic inequalities in health. Little is known however, about health promotion strategies particularly effective in lower socioeconomic groups in youth. It is the purpose of project TEENAGE to improve knowledge on the prevention of socioeconomic inequalities in physical activity, diet, smoking and alcohol consumption among adolescents in Europe. This paper describes the background, design and methods to be used in the project. Methods/design T...