The Otago prison medical service says nearly every inmate goes out in better health than that in which they arrrived, even if they complain about their care.
Radio New Zealand has revealed the police are investigating the care of an Otago prisoner who died in February 2011, and are reviewing another inmate's suicide four months earlier.
During a visit to the Otago Prison's health service by the public broadcaster, staff said it would be very rare to see an inmate getting out who hadn't had his health care improved while inside.
Corrections' director of offender health Bronwyn Donaldson says prisoners have high expectations, which are hard to meet.
"Some people's experience of health care will vary from place to place. But what I think I'm hearing, actually they do get good health care, it's just they won't always be happy about it."
Ms Donaldson says many improvements have been made to prison health services in the past three years.