Around 10% of Irish adolescents suffer from a major depressive disorder, according to figures released by the support group Aware.
According to the group, children are equally at risk of depression, but girls are twice as likely to develop the condition during adolescence.
Most of those affected are from families with a history of depression and, although the recovery rate is high, the condition is likely to recur.
Doctors believe early diagnosis is vital because 80% of sufferers benefit from treatment.