Seven people are to be prosecuted over the alleged ill-treatment of patients at Muckamore Abbey Hospital in County Antrim.
The hospital on the outskirts of Antrim is run by the Belfast Health Trust.
The Public Prosecution Service (PPS) said the families of patients have been informed about the development.
Fifteen people have been arrested since a major police investigation began in 2017 into alleged abuse at the hospital.
These are the first charges to be announced and it is understood all seven people are staff members at the psychiatric intensive care unit at Muckamore Abbey Hospital.
They are to be charged with offences including alleged ill-treatment and wilful neglect of patients at the unit.
The PPS said another eight people had been reported to them in a second investigation file, which remains under consideration.
It said decisions about whether or not to prosecute would be made "after a thorough consideration of all the available evidence".
The process had been difficult for the patients and their families who had shown "great dignity", added the PPS.
Chief Supt Anthony McNally of the Police Service of Northern Ireland said the decision to prosecute was "significant progress" in the investigation.
"This has been a very detailed and complex investigation and we will continue to work closely with the PPS," he said.
"Our specially-trained officers will continue to provide support to the families whose loved ones are at the centre of this investigation.
"From the outset we have been committed to working closely with them with the aim of keeping them as informed as much as we possibly can and we will continue to do so.
"The protection of our most vulnerable is a priority for the Police Service of Northern Ireland."