The Abuse in Care Inquiry believes there may be more than 100 unknown people who spent time at the Lake Alice Psychiatric Hospital's child and adolescent unit.
It was revealed last year the number of people abused in care since 1950 was up to 253,000, with the number of people passing through care being six times more than previously thought.
The Lake Alice child and adolescent unit operated from 1972 to 1978. It is known abuses – including sexual, physical and psychological - happened at the Manawatu-based unit and the Inquiry is concerned there are people it does not know about.
An Inquiry investigation into the unit indicates a far higher number of patients were admitted than previously thought. At redress hearings last year, the Health Ministry told the Inquiry's Commissioners it had not been able to make a complete list of patients.