Jayne Brown said hospitals had been extraordinarily busy
North Yorkshire's NHS trust is predicting that it will be £8m in the red by the end of the financial year.
The forecast by the North Yorkshire and York NHS Trust comes 12 months after it rid itself of a massive cash deficit.
The trust had an £18m deficit, the biggest of any primary care trust in England, in the year to March 2008, but balanced its books last year.
Chief executive Jayne Brown said the predicted figure of £8m was "very disappointing".
The trust said the deficit was less than 1% of its annual £1.2bn budget, but admitted that it was "not an acceptable position".
It said it would try to make further savings to reduce the figure before the end of the financial year.
Finance director Nick Steele told BBC News: "I can't guarantee that there won't be any changes in services.
"Certainly what we'd look to do is redesign services to not only improve patient care but to actually do that at a lower cost."
Ms Brown said her colleagues across the county had "worked so hard to control spending whilst delivering excellent health care services - something that the public have recognised us for in a recent satisfaction survey".
She added: "We continue to improve in all areas of our work and we will not allow this issue to divert our focus from quality of provision based on best evidence."
Ms Brown said the main reason for the deficit was that its hospitals had been "extraordinarily busy" and had dealt with "many more patients than we could have predicted when we were drawing up spending plans".
She said the trust had also seen "escalating costs of secure forensic mental health services, continuing care and prescribing".