The Southern Health and Social Care Trust, which includes the Dungannon District, has spent almost £5million on taxis and buses for patients in the last five years.
Although the annual bill has dropped since 2010, from £1.2m to £890K, it is still the second highest in the North.
The South Eastern Trust racked up the highest cost at £1m last year, while the Western Health and Social Trust ran up the smallest transport bill at £739,455.
A spokesperson for the Department of Health said the taxis were used for a variety of reasons.
Most of the expenditure was incurred on the transport of vulnerable patients and clients, particularly children in care and adults with a physical or learning disability.
“The use of taxis by Health and Social Care Trusts is planned and monitored”, added the spokesperson.
The bill has angered health service unions who claim the money could be better invested in front line staff and improved services.
Joe McCusker, regional organiser with Unison, said: “We certainly are shocked and alarmed that so much money is being spent. There needs to be an examination into whether or not these costs are viable and justified.
“Why can the money not be spent being invested in consultants and proper resources here in Northern Ireland for the people who need it?”
The taxi bills for Northern Ireland’s health trusts were elicited by David McNarry UKIP MLA for Strangford from the Department of Health.
Local trusts have had to pay transport and accommodation costs for patients transferred to hospitals in the Republic for non-emergency operations in a bid to cut waiting times or because procedures could not be carried out in Northern Ireland, according to health department officials.
Flights, taxis and hotels have cost the Belfast Health and Social Care Trust £3,001,049 since 2008..