The review, carried out by George Reid, the former presiding officer of the Scottish Government, concludes that the charity is "not sustainable as presently organised".
It says that in addition to radically reforming its "byzantine" governance structures, the organisation needs a strategic plan because it "lacks a common purpose".
The report says: "There are 87 trustees and, additionally, there are over 100 non-executives engaged in the work of its panels and committees.
"Its decision-making is largely gridlocked – we have been unable to find any other charity with such inflated governance structures. We believe they prevent the trust tackling issues and setting strategic direction."
Reid’s review, which was carried out after concerns were raised about the trust’s finances, also says the NTS must "reaffirm its core purpose" as a conservation charity.
"A new mission statement should be prepared and agreed with members at the 2011 AGM, focusing on the trust’s unique identity and common cause," the review concludes.
The review also recommends that the trust develop a proper inventory – in the form of a single database or document – of what it owns, and suggests that it might have to reduce the size of its property portfolio.
"At some point, it may well be that NTS will have to concentrate on a smaller core portfolio. Deciding what that is will take time and consultation," the review says.
"Currently, NTS has no single inventory of what it owns. There has to be a systematic portfolio review that identifies core properties to be fully managed by the trust, and other properties suitable for alternative management."
Kate Mavor, chief executive of NTS, said the review team had correctly identified that the trust had been over-governed for far too long.
"The trust’s management has been held back through the existence of such a top-heavy structure," she added.
Mavor also acknowledged that the trust might need to cut its property portfolio. "We fully recognise that the trust cannot conserve the nation’s heritage entirely on its own – we therefore fully support the review’s proposal of partnerships with other bodies," she said.
A spokesman for In Trust for Scotland, a group of more than 2,500 concerned members of the NTS, said: "We are glad George Reid endorses our call for a radical shake-up of the trust’s governance and a reduction in the number of trustees.
"His revelation that the trust had no complete inventory of its properties and moveable assets comes as a shock, but no surprise, in an organisation that had been poorly led for some time.
"We note the commitment of the chief executive to rectify this as part of a long overdue, thorough audit. Members and volunteers continue to be concerned about the whereabouts of assets at certain properties."