The centre detains people who are found not guilty of a crime by reason of insanity.
Patients spend an average of eight years in the Central Mental Hospital before being discharged.
The centre detains people who aren't fit to stand trial, or are found not guilty of a crime by reason of insanity.
There are normally around 80 or 90 patients detained in the Central Mental Hospital in Dundrum in Dublin.
They include Deirdre Morley. She killed her three children - Conor, Darragh and Carla McGinley - at their home in Newcastle in Co Dublin, two and a half years ago, though she was found not guilty of their murder by reason of insanity.
Patients are reviewed every six months to see if they're fit for discharge.
Last year six of the 87 patients assessed by the Mental Health Review Board were allowed to leave.
They had spent an average of eight years in detention.
Of the 87 patients reviewed last year, 62 per cent had schizophrenia and nearly half had been charged with, or convicted of, murder.
The Dublin hospital detains people who aren't fit to stand trial, or are found not guilty of a crime by reason of insanity.
Consultant psychiatrist, Patricia Casey, says they are patients with very severe mental illnesses: