One in ten teenage girls harms herself each year, according to the largest study of self-harm among 15 and 16-year-olds in England.
The problem is far more widespread than previously believed and girls are almost four times more likely to be involved than boys.
Researchers found 11 per cent of girls and three per cent of boys reported that they had self-harmed within the previous year.
Academics said teenagers were often motivated by distress, and self-harm was more common in those who had been bullied or subjected to physical or sexual abuse.
Cutting was the most common form of abuse (65 per cent), followed by overdosing (31 per cent), according to the study.
The findings were the result of a survey of 6,000 school pupils at 41 schools in Oxfordshire, Northamptonshire and Birmingham in 2000 and 2001.
They have been published in a book, By Their Own Young Hand, which includes practical advice for teachers on how to detect young people at risk.
Author Dr Karen Rodham, of the psychology department at Bath University, said: "The study shows that deliberate self-harm is common amongst teenagers in England, especially in girls, who are four times more likely to self-harm than boys. Until now, most studies of deliberate self-harm in adolescents in the UK have been based on the cases that reach hospital.
"We have found that the true extent of self-harm in England is significantly wider than that."
The previous estimates of those involved in self-harm was based on about 25,000 people who visited hospital each year for treatment.
But researchers believe there is huge under-reporting as they found just 13 per cent of self-harming incidents reported by pupils resulted in a hospital visit.
Professor Keith Hawton, of the Centre for Suicide Research at Oxford University, directed the research project.
He said: "This study provides more information about why young people engage in deliberate self-harm and helps us to recognise those at risk, to develop explanatory models and to design effective prevention programmes.
"In many cases, self-harming behaviour represents a transient period of distress, but for others it is an important indicator of mental health problems and a risk of suicide.
"It is important that we develop effective school-based initiatives that help tackle what has become a most pressing health issue for teenagers."