Shock figures show that health boards in the north and north-east have spent more than £215million on agency staff in the last decade.
Data released to the Scottish Conservatives sparked fresh concerns over the “long-term reliance” on agency staff at “very high cost” in the nation’s NHS.
And a patients group said the figures were symptomatic of the “continued underfunding” of the region.
The statistics also show sharp rises in some areas, with NHS Grampian having the second highest bill in Scotland last year, after only Greater Glasgow and Clyde.
The north-east board spent £23.1million in 2016/17, a rise of more than £4million on the previous year, with the total having increased dramatically in every year since 2011/12, when £3.8million was handed over to agencies.
The figure for the last year accounted for more than a quarter of the £80.8million spent by NHS Grampian over the last 10 years.
Meanwhile, agency workers cost NHS Highland almost £16.4million last year, also the highest figure recorded by the north board in the past decade, with the total bill for the period reaching £91million.
NHS Orkney spent £2.25million last year and £9.77million over 10 years, while Shetland forked out £2.4million in 2016/17 and £16.9million over the period. NHS Western Isles spent £2.7million, with a total bill of £17million for the decade.
Scottish Conservative shadow health secretary Miles Briggs said: “Agency staff are really important in our NHS as they are flexible and can fill short-term staffing gaps, as well as reducing waiting lists.
“However the SNP mismanagement of the NHS has clearly led to a long-term reliance on agency staff at very high cost.”
Professor Jamie Weir, of patient group Pact, said: “Recruitment and retention are known major problems in the North and North-East, partly because of the continued underfunding given to these regions, but also the stresses caused by the increased responsibilities and workload placed upon the remaining permanent staff.”
But a Scottish Government spokesman said staffing levels were at a “record high” in Scotland.
The spokesman said: “All NHS boards have clear action plans in place to reduce the use of agency staff further, as well as arrangements to ensure that when staff are required, agency are the last resort.”
NHS Grampian has said agency staff play a vital role in filling service gaps.