During the transition to adulthood, so often a source of concern, health is rarely the main preoccupation among young people. Most state that they are in good health and fairly well informed in terms of prevention. However, this transition towards independence, punctuated by experimentation, can weaken their physical and mental state of health. Addictions, eating disorders, dangerous driving, all such behaviour does not necessarily expose young people to an immediate risk of death but all can have repercussions on their health, from social marginalisation to heightened risks of illnesses and psychological disorders in adulthood. Recent developments demand vigilance. The daily consumption of tobacco has taken off since 2008. Today, nearly one third of people of 17 years of age smoke every day. Instances of drunkenness have increased since 2005, especially among girls. At 17 years of age, more than one out of two admitted to having been drunk in 2011. Moreover, the prevalence of being overweight and obese has increased since the 2000s among those aged 18-24. In this quest for breaking the rules, boys paid a heavy price with around 2,300 deaths among those aged 15-24 in 2010, deaths associated with violence (road accidents and suicides). Among girls, the body is the expression of their ill-being: in the fourth year of secondary school, 42% see themselves as being too “fat”, a dissatisfaction that can lead to eating disorders and suicidal thoughts or even attempted suicide (2% of girls aged from 15 to 19 in 2010).