The first day of public hearings in the Muckamore Abbey Hospital Inquiry is under way in Belfast.
The inquiry is examining allegations of abuse of patients at the facility in Co Antrim.
Proceedings on Monday started with an opening statement by chairman Tom Kark QC.
He previously played a key role in the 2010 inquiry into avoidable deaths at Stafford Hospital.
I believe it is appropriate today for me to publicly reiterate my previous apology on behalf of the health and social care system to all the patients and families who have been so badly let downStormont Health Minister Robin Swann
The inquiry is also set to hear an opening statement from senior counsel to the inquiry Sean Doran QC.
Opening statements from core participants are expected to be heard on Wednesday and Thursday.
Relatives of patients were among those who attended the inquiry on Monday.
Glynn Brown, whose son Aaron had been a patient at the hospital, was among those who turned out.
Mr Brown, who previously raised the alarm about the facility, said he will be watching to see if the “depth and scale” of what happened will be uncovered, and what will be done about it.
Muckamore Abbey is a hospital for adults with severe learning disabilities and mental health needs.
Following a lengthy police investigation into claims of patient abuse at the facility, which is operated by the Belfast Health and Social Care Trust, it was announced last year that a number of people are to be prosecuted for alleged mistreatment of patients.
It has been described as the UK’s largest ever police investigation into the alleged abuse of vulnerable adults.
Speaking ahead of the first day of public hearings, Stormont Health Minister Robin Swann said he trusts the inquiry will provide the answers needed.
“I have no doubt that the inquiry proceedings will be a harrowing experience for all those affected by the abject failure of care at Muckamore. It will also be deeply distressing for everyone who works in health and social care in Northern Ireland,” he said.
“I believe it is appropriate today for me to publicly reiterate my previous apology on behalf of the health and social care system to all the patients and families who have been so badly let down.
“As I stated in September 2020 when I announced my intention to establish an inquiry, patients and families need more than apologies.
“They deserve the truth on what has happened and how it was allowed to happen. I trust that this public inquiry will provide the answers that are required.”