Unions have warned there must be no cuts to front-line services
The health service in Scotland will face "significant" financial pressures over the next five years, a spending watchdog has predicted.
Audit Scotland said the impact of the recession on public sector spending meant NHS budgets were likely to fall.
It also warned the country faced some deep-seated health problems that the health service alone could not tackle.
But it said the financial performance of the NHS in Scotland had been "good" over the past year.
The Audit Scotland report said the NHS had met most of its national targets for patient care and service improvement in 2008-09.
All of Scotland's NHS boards met their financial targets, and the health service had an overall £4m underspend.
The report also said people in Scotland were living longer, and some key indicators of health were showing improvement.
However, it said the current financial year was likely to see public spending "peak", with budgets expected to reduce in real terms over the next five years.
The NHS can only help tackle problems such as teenage pregnancy and drug abuse in partnership with education and social services, it added.
Auditor General for Scotland, Robert Black, said the health service met 10 out of 13 performance targets in the past year, including reducing cancer treatment waiting times.
He said: "The financial performance of the NHS in Scotland continues to improve, with all bodies meeting their targets in 2008/09 and the service finishing the year with a small underspend.
"However, the service faces real pressure, from both existing cost pressures and from the impact of the recession on public sector spending.
"As the amount of public money available reduces in coming years, the NHS will need to ensure that it continues to provide good quality care while becoming more efficient, and it should make sure it is getting the information it needs to achieve this.
His concerns were echoed by Dr Brian Keighley, chairman of the BMA in Scotland, who said the drive to meet targets for 2% efficiency savings would become increasingly difficult.
He said: "Government must protect frontline health services to ensure that funding cuts will not impact on patient care."
Theresa Fyffe, director of nursing union RCN Scotland, said it was "concerning to patients and staff" that some health boards were already reporting overspends during the current financial year.
Health Secretary Nicola Sturgeon said the Audit Scotland report showed that "we can all celebrate the significant achievements" of the NHS.
She added: "There is no doubt that the entire public sector faces a challenging climate ahead, but the Scottish government's draft budget for 2010-11 has protected health spending, which is set to rise to £11.347bn.
"While we cannot predict the public spending environment beyond the next Spending Review, NHS Scotland is working hard now to become leaner and more efficient so that we are prepared to deal with whatever lies ahead."
Labour's Jackie Baillie said: "There is no doubt that frontline services will be at risk. This report is deeply worrying. The health secretary needs to make sure that the NHS has sufficient funding to avoid these swingeing cuts, otherwise vital frontline services will be affected."
Scottish Conservative health spokesman Jackson Carlaw MSP said the findings "blow apart the SNP's strategy of creating a fortress NHS that shuns private enterprise and other health providers".
While Scottish Lib Dem health spokesman Ross Finnie said the report was a "stark warning" that the Scottish government's cuts to the NHS budget could start to affect patient care as early as next year.