Most of the adolescents enjoy good physical and mental health. However, the incidence and prevalence of chronic diseases in adolescence are on the rise and likely are due to an earlier onset of obesity-associated disorders, longer survival after serious childhood disorders, and other unknown factors. The most common problems among adolescents relate to growth and development, school, childhood illnesses that continue into adolescence, mental health disorders, and the consequences of risky or illegal behaviors, including injury, legal consequences, pregnancy, infectious diseases, and substance use disorders. Unintentional injuries resulting from motor vehicle crashes and injuries resulting from interpersonal violence are leading causes of death and disability among adolescents. Psycho social adjustment is a hallmark of this phase of development because even normal individuals struggle with issues of identity, autonomy, sexuality, and relationships. “Who am I, where am I going, and how do I relate to all of these people in my life?” are frequent preoccupations for most adolescents. Psycho social disorders are more common during adolescence than during childhood, and many unhealthy behaviors begin during adolescence. Having an eating disorder, poor diet, obesity, smoking, using drugs, and violent behavior can lead to acute health problems, chronic disorders, or morbidity later in life.