Purpose of review To provide an update of the recent studies on the age of onset of the major mental illnesses, with a special focus on the prospects for prevention and early intervention. Recent findings The studies reviewed here confirm previous reports on the age of onset of the major mental disorders. While the behaviour disorders, and certain anxiety disorders, emerge during childhood, most of the high prevalence disorders (anxiety, mood and substance use) emerge during adolescence and

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... y adulthood, as do the psychotic disorders. Early age of onset has been shown to be associated with a longer duration of untreated illness and poorer clinical and functional outcomes. Summary Although the onset of most mental disorders usually occurs during the first three decades of life, effective treatment is typically not initiated until a number of years later. Although there is increasing evidence to suggest that intervention during the early stages of a disorder may help reduce the severity and/or the persistence of the initial or primary disorder and prevent secondary disorders, additional research is needed into appropriate treatment for early stage cases as well as the long-term effects of early intervention, and to appropriate service design for those in the early stages of a mental illness. This will mean not only the strengthening and re-engineering of existing systems but also, crucially, the construction of new streams of care for young people in transition to adulthood.