The Audit Scotland report warns the NHS north of the border will not be able to provide the same level of service in the future unless urgent action is taken.
Tightening budgets, rising costs, higher demand, pressure to meet targets and increased staff vacancies are all cited as factors in what opposition politicians believe is a deepening crisis.
The report also says the Scottish Government has not made sufficient progress towards its 2020 vision to change the balance of healthcare to more community-based settings.
Doctors said “substantive action” was needed to address the report’s findings, while opposition parties called for SNP ministers to “get a grip” on the NHS.
Audit Scotland found health boards missed seven out of nine key waiting time targets and standards at March 2015, “reflecting a general decline in performance in recent years”.
Boards spent £284million on temporary staff in 2014-15 – an increase of 15% from the previous financial year.
The number of agency nursing and midwifery staff increased by 53%, while spending on locum doctors increased by 22%.
Caroline Gardner, auditor general for Scotland, said: “We all depend on the NHS and its staff who provide high-quality care.
“But it will not be able to provide services as it does at present due to the number of pressures it faces within the current challenging financial environment.”
Dr Peter Bennie, chair of BMA Scotland, said: “The overriding message that must get through from this report is that substantive and realistic action is needed if our health service is to cope with the rapidly increasing pressures it is facing.”
Royal College of Nursing Scotland associate director, Ellen Hudson, said: “If we are to put the NHS on a sustainable footing, then the government needs to take heed of the recommendations in this report.”
Health boards spent a total of £11.4billion, ending the year with an underspend of £10 million.
The report said the health budget had decreased by 0.7% in real terms between 2008-09 and 2014-15.
Liberal Democrat health spokesman Jim Hume said: “The findings of this latest report are stark – unless SNP ministers get a grip, the 2020 vision will not be achieved.
“NHS boards have been forced to scramble to address staff shortages and short-term arrangements have replaced long-term planning. This is clearly not sustainable.”
Conservative health spokesman Jackson Carlaw said: “Patients deserve far better and the NHS needs far more support, which is why Scottish Conservatives have promised an additional 1,000 nurses, not 1,000 empty SNP words.”