Gordon McLean, a frail, 63-year-old with schizophrenia and dementia, was living at the hospital when he went missing on October 12.
Mr McLean left the hospital that day, and an extensive police search failed to find him.
On Tuesday, another Wakari resident was reported missing, after being seen leaving the hospital grounds about 6am.
Police said the 59-year-old man was returned safely to hospital yesterday morning.
The Southern DHB has carried out an internal investigation into Mr McLean's care and how he managed to leave the hospital undetected.
DHB mental health general manager Louise Travers called Mr McLean's disappearance a serious event.
''As is procedure ... the SDHB has commissioned an external review. This review is scheduled for March,'' she said.
The review will be the responsibility of the chief medical officer.
Usually, a senior clinician from another DHB is asked to carry out such reviews.
Mr McLean had lived in a non-secure rehabilitation facility at Wakari.
Police scoured the immediate vicinity of the hospital as well as nearby Frasers Gully, Halfway Bush and Helensburgh but found no trace of him.
A police spokeswoman said Mr McLean's file remained active, and police were still looking for new information and following up any reported sightings.
''A significant amount of police and volunteer hours went into what amounted to a very comprehensive search of the surrounding area where he was last seen.
''However, it has failed to show any sign of Gordon ... the search phase has concluded pending new information.''
Mr McLean was last seen wearing a dark polar fleece, trousers, a red polo shirt, brown slippers and a black puffer vest.
