Foreign patients treated in New Zealand hospitals owe the system at least $19 million.
The Herald on Sunday asked the 20 district health boards under the Official Information Act how much they were owed by non-New Zealand residents ineligible for free treatment.
Thirteen responded within the statutory deadline of 20 working days.
They owed $18.9 million with Counties Manukau having the biggest debt ($6.3m), followed by Auckland ($3.9m), Waikato ($1.9m) and Waitemata ($1.2m).
Amounts owed to boards which failed to respond are expected to tip the total well beyond $19m.
The largest bill racked up by an individual patient was in Auckland and cost the board more than $500,000.
Boards attempt to recover debts by organising payment plans and, in some cases, enlisting debt collectors.
Most boards have started toughening up on patient eligibility. Waitemata announced this year all patients with non-urgent issues would have to produce a birth certificate or passport from July.
A spokesman said the board spent $200,000 a year checking eligibility and estimated over the next year it would recover enough to fund 640 elective surgeries.
Starship children's hospital director Dr Richard Aitken said funding treatment for ineligible patients was a sensitive topic.
Front-line staff were more concerned with a patient's condition but the cost to the health system was a consideration.
"If someone turns up to the ED [emergency department] their immediate needs are met ... people should know that ED services are always available to everyone."
He said ongoing treatment or non-urgent appointments would only be agreed once payment was discussed.
Doctors or nurses may also tell foreign patients that treatment could be cheaper at an accident and emergency clinic.
It is understood emergency visits to public hospitals cost about $300 with an overnight stay costing more than $2000.
Aitken was unable to say where most ineligible foreign patients were from.
Grey Power Auckland spokesman Jens Meder said his organisation believed all patients should provide proof of residency before receiving free treatment. The outstanding amounts could be used to fund surgery for Grey Power members who "have been paying their taxes for years".
He said there was a case for treating people with potentially fatal injuries from an accident. "But if there is free hospital treatment for everyone then we become like the soft touch and anyone can just come over here and have operations."
Daughter shocked by visitor's debt
The daughter of a Briton deported from New Zealand in case he needed publicly funded medical care is upset by the debt run up by foreign patients.
Martyn Payne and his family moved to New Zealand six years ago and invested $700,000 in a garage in the Northland town of Kapiro. He was forced to leave after his application for residency was declined on health grounds.
He has had surgery for a heart condition, which his doctors believe will not cause him problems but the Immigration Service fears could cost the health system $25,000.
More than 1200 supporters have signed a petition and the Motor Trade Association has hired an immigration agent to fight his case.
His daughter, Nicola, said her family hadn't cost Kiwi taxpayers a cent in health treatment since migrating.
"If I or the kids need to go to the doctor, we pay for it."
She was shocked one foreign patient in Auckland had run up a debt of more than $500,000.
Nicola said her father was with friends in Brisbane and having more tests to convince New Zealand authorities to let him return for good.