This international report is the fourth from the Health Behaviour in School-aged Children (HBSC) study, a WHO collaborative cross-national study, and the most comprehensive. It presents the key findings on patterns of health among young people aged 11, 13 and 15 years in 41 countries and regions across the WHO European Region and North America in 2005/2006.Its theme is health inequalities: quantifying the gender, age, geographic and socioeconomic dimensions of health differentials. Its aim is to highlight where these inequalities exist, to inform and influence policy and practice and to help improve health for all young people.