Allegations of physical and sexual abuse at an adolescent mental health unit spanning decades are being investigated, police said.
A criminal investigation into reports of abuse of young patients at Hill End Hospital Adolescent Unit in St Albans, Hertfordshire, has been launched, Hertfordshire Constabulary said.
The abuse is said to have taken place between 1969 and 1995, when the unit closed, and the force said the number of possible victims involved was "unclear".
A number of reports made to police in the past are being reviewed by officers as part of Operation Meadow, the force said.
No new reports have been made to police at this stage.
Assistant Chief Constable Bill Jephson said: "Hertfordshire Constabulary takes all reports of child abuse seriously, no matter how long ago the offence may have occurred.
"We have officers who are specially trained to deal with these type of crimes while supporting victims in a sensitive, empathetic and caring manner."
Anyone with information or who thinks they may be a victim should contact the force via 101 or an online form, or Crimestoppers anonymously on 0800 555 111.
Copyright (c) Press Association Ltd. 2017, All Rights Reserved.