Epidemiologists pored over data from the 2.6 million deaths that occurred among the world's population of 1.8 billion aged between 10 and 24 in 2004.
Road accidents accounted for 10 percent of the deaths; suicide 6.3 percent; violence 6.0 percent; lower-tract respiratory infections and TB 11 percent and AIDS 5.5 percent.
The study highlighted major differences according to region.
Nearly two-thirds of the premature deaths occurred in sub-Saharan Africa and Southeast Asia, and only three percent occurred in rich countries.
Botched abortions and female genital mutilation in poor countries were big factors. "Maternal mortality," which includes death from those and other practices, accounted for 15 percent of deaths among teenage girls and young adult women.
The study was headed by George Patton at the Royal Children's Hospital, Melbourne, Australia; Russell Viner at University College London; and Krishna Bose of the World Health Organization (WHO).