A wide ranging review of health services has been launched on Teesside.
Health bosses say they are "not ruling anything out" in a drive for greater efficiency.
The scale of the review is bound to lead to speculation about possible hospital closures, particularly when the new superhospital in Middlesbrough opens later this summer.
But the more likely outcome of any changes is the concentration of particular clinical specialisms, leading to the closure of services at other sites.
Hospitals in Stockton and Hartlepool would appear to be potentially vulnerable to services being switched to the expanded James Cook University Hospital in Middlesbrough.
This could lead to patients having to travel further for treatment for specific health problems.
Health bosses have warned that the need to improve the quality of treatment by concentrating services will almost inevitably mean sweeping changes.
Details of any proposals will not be known until December when they will be subject to public consultation and scrutiny by new local authority watchdogs.
If the proposals stir up a storm of public opposition the new scrutiny panels could refer them upwards to a health minister for a final decision.
In launching the six month review, Ken Jarrold, chief executive of County Durham and Tees Valley Strategic Health Authority, said: "This is a very important day for the Health Service on Teesside."
He said "the big issue" for Teesside was the sustainability of hospital services north of the river.
Last year a mini-review of hospital services recommended that hip and knee patients in Stockton would have to travel to Hartlepool for treatment and Hartlepool cancer patients would travel to Stockton for care.
Mr Jarrold said this much wider review was necessary because the NHS had very ambitious targets for reducing waiting lists and treating more patients which could only be met by changing the way services are delivered.
"This will require us to use all the extra resources we have been given by the Government to the best effect," he added.
The opening of state-of-the-art modern facilities at James Cook would inevitably lead to a reassessment of hospital facilities north of the river, said Mr Jarrold.
"We have the splendid new James Cook site opening this summer, we have to look at the consequences of that for hospitals north of the river. We also need to look at the relationship between the Friarage Hospital in Northallerton and the new hospital in Middlesbrough."
Mr Jarrold said it was important not to think of the changes as being purely concerned with centralisation.
"We also have to ask whether there are things that are better done in primary care. We now see specialist GPs, nurses and other health professionals providing a ragne of care which would not have been done 15 years ago," he added.
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