In 2015, more than 1.2 million adolescents died and accidents were to blame for about one in 10 of these deaths, the BBC quoted the WHO as saying.
Males aged 15-19 make up the biggest share of these 115 302 fatalities, mostly in poorer countries in Europe, the Americas and the Eastern Mediterranean region
Most young people killed are "vulnerable" road users: pedestrians, cyclists and motorcyclists.
Chest infections and self-harm were the biggest global killers of girls and young women, however.
Deaths from self-harm are increasing in many regions, says the WHO report author, Anthony Costello.
"Self harm is a massive and increasing issue in many countries. We are seeing suicide rates go up.
"Adolescence is quite a stressful time of life. Young people need support, but adolescent health across the world has been largely neglected," the BBC quoted the author as saying.
According to the worldwide report, more than 3000 adolescents die every day.