The organisation which oversees many of Scotland's historic properties needs a clear-out to make it "fit for purpose", a review has found.
The National Trust for Scotland should slash trustee numbers from 87 to 15 and elect a new board, former Holyrood presiding officer George Reid said.
Mr Reid was called in by the trust to look at its long-term future after it was hit with serious cash shortages.
The trust has fully endorsed the recommendations of the review.
The National Trust for Scotland plays a crucial role in protecting and promoting cultural heritage and oversees more than 100 sites, including Culloden Battlefield and the islands of St Kilda, a world heritage site.
But the body, which employs 456 permanent and 755 seasonal staff, was forced to embark on a major cost-cutting programme after being hit hard by the recession and falling visitor numbers.
Chairwoman Shonaig MacPherson also stepped down last September amid accusations members were being kept in the dark about financial problems.
The trust eventually sold its Edinburgh headquarters, mothballed three historic properties and cut posts.
Delivering the results of his nine-month review, involving 12,000 members, Mr Reid said the trust was not sustainable if it continued to operate in its present form.
He said the National Trust had no single inventory of its assets, and did not know the cost of maintaining its estate.
Position 'not sustainable'
His five recommendations to make the National Trust for Scotland "fit for purpose" also included putting a new board in place by next April, a full audit of the organisation's properties and a new "mission statement" and five-year strategic plan.
"The immediate issue is clear," said Mr Reid, adding: "The trust balances its books by using legacies as ready income, by selling assets and by delaying project work.
"It has no single record of what it owns. It does not know the cost of repairing and maintaining its estate. Its current budget was prepared on a needs-must basis.
"That is not a sustainable position."
The review pointed out the trust was operating a dual system of governance, with 87 trustees serving on its board and council, while about 100 non-executives served on various panels and committees.
And there were 35 representative members from other organisations on the council.
National Trust for Scotland chief executive Kate Mavor, said: "George Reid and his review team have correctly identified the trust has been heavily over-governed for far too long and that its management has been held back through the existence of such a top-heavy structure.
"For our part, we firmly believe the reforms to the governance of the charity can be introduced within the timescale set.
"We also believe change is essential to take the National Trust for Scotland forward and meet the important conservation challenges ahead."
The chief executive added that the trust's latest accounts showed it to be in a "more stable financial position".
National Trust for Scotland president, The Duke of Buccleuch, said: "We face urgent challenges, but thanks to the speed with which Mr Reid worked, there is now a clear route map for reform to put to National Trust for Scotland members at their AGM in September."
Welcoming the report, Culture Minister Fiona Hyslop, said: "The immediate priorities for the trust are to manage its functions more effectively to protect the national heritage that has been entrusted to it.
"The Scottish government believes there needs to be more effective and sustainable partnerships developed by the trust with other heritage organisations such as Historic Scotland and I am keen to see that fostered."
The historic environment sector is said to be worth more than £2.3bn to the economy and supports 40,000 jobs.