The death is not suspicious and will be referred to the coroner.
In a joint statement Vicki Aitken and Dr Rees Tapsell, respectively the executive director and director of clinical services for the Waikato District Health Board's Mental Health & Addictions Service, said they couldn't confirm the circumstances of the man's death due to patient and family privacy.
However, they confirmed "he was an inpatient who was at the stage of transitioning to live in the community, he did not return from his 'approved' unescorted leave Sunday morning".
"We can say that once it was clear that he had not returned as arranged, and was not in the immediate environs of the Henry Rongomau Bennett Centre, the police were notified and staff worked closely with the police and family in attempting to locate him.
"Any death like this is a tragedy for the family and we are now supporting them through this difficult time, as well as supporting our staff."
The DHB would conduct a review into the death.