Unpaid bills racked up by foreign patients at New Zealand's largest health board rose by a third to $18 million last year.
It left a $4.5 million black hole in the Auckland District Health Board's budget for the 2010/11 financial year.
Bad debt written off by the Counties Manukau District Health Board also jumped, to $5.4 million in the eight months to February 2012, up from $1.7 million the previous financial year.
Chief financial officer Brent Wiseman said increases were mainly the result of population growth and high numbers of overseas visitors passing through Auckland.
"[ADHB] has one of the highest amounts in the country of gross charges to ineligible patients due to its position as a key destination and transit point for visitors to New Zealand," he said.