Road traffic accidents, not Aids, cancer or any other disease, are the biggest killer of young people worldwide, experts warn.
Over 1.2m people are killed in road crashes around the world annually
Nearly 400,000 young people under the age of 25 are killed in road traffic crashes every year. Millions more are injured or disabled.
Most occur in low income countries, such as Africa, and are avoidable.
The World Health Organization's report comes ahead of the first UN Global Road Safety week beginning next week.
The "Youth and Road Safety" report stresses that the bulk of crashes are predictable and preventable.
Many involve children playing on the street, young pedestrians, cyclists, motorcyclists, novice drivers and passengers of public transport.
Driving under the influence of alcohol is also a problem.
WHO says a number of measures have helped reduce the number of deaths and injuries significantly in high income countries, including the UK.
These include lowering speed limits, cracking down on drink-driving, promoting and enforcing the use of seat-belts, child restraints and motorcycle helmets, as well as creating safe areas for children to play.
Dr Etienne Krug, director of the WHO's Department of Injuries and Violence Prevention, said: "Shockingly road traffic crashes are the biggest killer of young people. That's ahead of diarrhoea, malaria, TB and HIV.
"We can do something about this."
Dr Margaret Chan, WHO Director-General said: "Road traffic crashes are not 'accidents'. We need to challenge the notion that they are unavoidable and make room for a proactive, preventive approach."
In the UK, 91 people are killed and seriously injured every day on the roads, of whom more than a third is under 25, according to the UK's national road safety charity Brake.
It wants the UK government to invest more in road safety and will be launching its manifesto on Monday, demanding urgent action.
Jools Townsend, head of education at Brake, said: "It is high time UK and world leaders made making roads safe a top priority."
A Department for Transport spokeswoman said: "Britain has made good progress in improving road safety and as a result has some of the safest roads in the world.
"However we fully appreciate that even one death or serious injury is one too many."
She said areas where further work could continue to improve road safety included young drivers and speeding.
"As part of this we have already announced a fundamental review of the education, training and testing procedures currently in place for new or young drivers."