The long-awaited new Central Mental Hospital has opened in Portrane in north Dublin today.
Despite having room to house 170 beds, it will open with just 110 as there aren't enough staff.
It is the state's largest capital health project aside from the National Children's Hospital.
The old mental health hospital may be used for affordable housing in the future.
The 170-bed facility is being described as one of the best of its kind in Europe, complete with a women's only ward and a section for children and adolescents.
Speaking at the official opening today, Minister for Health, Stephen Donnelly TD said: "Today is a significant and historic day for the Irish health service.
"This fantastic new facility brings real and necessary change to the lives of some of the most vulnerable in our society. This opening reiterates the Government’s commitment that healthcare to this vulnerable group should be delivered on the same values, principles and approaches that apply to all others in society."
Patrick Bergin, Head of Service at NFMHS says: "The opening of the Central Mental Hospital in Portrane as part of the National Forensic Mental Health Service is a key milestone in the delivery of a modern forensic service to our patients.
"We now have the opportunity to be a centre of excellence and evolve our delivery of treatment and care for patients further. This is a welcome day for patients, family/ carers and our staff and this new facility provides us with opportunities to be a world leader in this specialist field."
