Adolescence is a transitional stage of physical and psychological human development that generally occurs during the period from puberty to legal adulthood. There are approximately 1.2 billion adolescents (10-19 years) globally, roughly 90% of whom live in low and middle-income countries. Most are healthy, but there is still significant death, illness and diseases among adolescents. Illnesses can hinder their ability to grow and develop to their full potential. Alcohol or tobacco use, lack of physical activity, unprotected sex and/or exposure to violence can jeopardize not only their current health, but often their health for years to come. The mortality rate decreased from 126 to 111 per 100 000 between 2000 and 2012. This modest decline of about 12% continues the trend of the past 50 years. Mortality rates dropped in all regions and for all age groups except 15–19 year old males in the Eastern Mediterranean and the Americas regions. The leading causes of death among adolescents in recent years were: road injury, HIV, suicide, lower respiratory infections, and interpersonal violence. Promoting healthy practices during adolescence, and taking steps to better protect young people from health risks are critical for the prevention of health problems in adulthood, and for countries’ future health and social infrastructure.