Patients groups said managers of boards were wasting money that should be spent hiring permanent staff, but ministers said the NHS had more employees than seven years ago.
Figures disclosed under Freedom of Information legislation revealed a 60% rise in spending on agency nurses across NHS Scotland in 2012/13. Health boards spent £6.2m - nearly £17,000 a day - bringing in nurses from private agencies to cover NHS shortages. This compared to £3.9m in 2011/12.
The biggest increase in spending was in NHS Forth Valley, where spending on agency nurses soared 20-fold from £14,000 in 2011/12 to £274,000 in 2012/13.
Meanwhile, locum doctors cost the NHS in Scotland £51.3m in the 2012/13 financial year - equivalent to more than £140,000 a day, and up from £41.5m the year before.
The three island health boards - Orkney, Shetland and Western Isles - spent £4.65m on locums, an indication of the boards' struggle to attract permanent GPs and consultants to remote areas. Only NHS Greater Glasgow and Clyde and NHS Lothian spent more.
Dr Jean Turner, executive director of the Scotland Patients Association, said: "It's economically inefficient to keep buying in locums and agency nurses because they are a lot more expensive than your permanent staff and NHS bank nurses.
"If management in any other company had to constantly bring in temporary cover then eventually they would realise it was more cost-effective to hire people and increase their core workforce.
"But part of it is about making the jobs more attractive. We need to look at the pay and conditions we're offering in the NHS. If a nurse can work a few days and week for an agency earning more money than working full-time, then why would they take a permanent job?"
It comes days after it emerged that an agency nurse hired by the NHS in England was paid £1800 for an 11 hour shift.
Ellen Hudson, associate director of the Royal College of Nursing (RCN) Scotland, said she was concerned about the increased spending on agency staff.
She said: "Prior to this use of agency nursing had been significantly reduced and RCN Scotland supports further efforts to curb expensive agency spending.
"At this time of increased financial pressure on the NHS, it is important that boards minimise use of agency nursing as much as practically possible by making sure they directly employ the right number of nurses with the right skills in the right places."
Dr Alan Robertson, member of the BMA's Scottish Council, said: "The availability of locums to provide short-term cover is important to the smooth running of our hospitals. They are not a substitute to good workforce planning and should not be used to plug long term gaps in medical rotas."
Liberal Democrat health spokesman Jim Hume, who uncovered the figures, said temporary staff were being used as a "sticking plaster" for the health service.
He said: "The Health Secretary is asking our NHS staff to do more and more and the system is creaking in many areas as a result of SNP mismanagement."
A spokeswoman for the Scottish Government said there were 6.3% more NHS staff now, excluding GPs and dentists, than in 2006.
She added: "We are working with health boards to establish local medical staff banks to help reduce spend on locums by allowing boards to share medical resources when needed. We will continue to promote their development and use across Scotland.
"The introduction of our mandatory nursing and midwifery workforce planning tools will also help boards ensure they have the right levels and type of staff in place."