More than 20,000 people were admitted to Irish psychiatric units and hospitals last year, according to figures published by the Health Research Board.
Seven out of ten were re-admissions, while the remaining 5,600 were first time admissions.
People aged between 45 and 54 were most likely to be admitted, with 18- to 19-year-olds most likely to be admitted for the first time.
The average length of stay was 27.5 days
Almost half of all discharges happened within two weeks, and nine out of ten within three months.
The report identifies a trend towards shorter periods of in-patient care, thanks to increased provisions of community care alternatives.
One in three cases relate to depression, one in five to schizophrenia and one in eight to alcoholic problems.
398 people under the age of 18 were admitted to psychiatric units last year.
The average duration of their stay was 23.2 days, although four in ten stayed less than a week.
Dr Dermot Walsh, a psychiatrist with the Health Research Board, says it is disappointing to see the number of people admitted to hospitals with depression.
Earlier, the Chief Executive of Mental Health Ireland expressed serious concern about the level of funding for Irish mental health services.
Speaking on RTÉ Radio's Morning Ireland, Brian Howard said €25m extra in funding had been promised per year towards the implementation of the Vision for Change document, which was published two years ago.
Mr Howard said that only a fraction of that money had gone into developing mental health services.
'We have a position today in late December 2007 where there's no extra money committed, no extra €25m, no development funds being committed to 2008, which to me is a matter of serious concern if we want to take the development of mental health services seriously,' he said.
