Health Secretary Nicola Sturgeon has ordered an investigation into procedures at NHS Ayrshire and Arran.
The health board had been severely criticised for withholding more than 50 reports on serious incidents at its hospitals and clinics.
NHS Ayrshire and Arran refused to release the critical incident and adverse event reports to staff.
The documents, released after a Freedom of Information (FOI) request, covered events including 20 patient deaths.
The FOI request was made by one of NHS Ayrshire and Arran's own nurses.
Ms Sturgeon has asked Healthcare Improvement Scotland to consider whether lessons can be learned for the rest of Scotland from events in Ayrshire.
The more serious incidents included in the documents involved three missed chances to diagnose cancers, the death of a patient who was trapped in a faulty lift, a death which followed inadequate treatment of a leg wound, and two cases where psychiatric patients murdered or attempted to murder a relative.
Critical incident and significant adverse event reports are compiled whenever anything goes wrong in the health service to establish exactly what happened and what can be done to prevent the mistakes being repeated.
However, for at least five years, NHS Ayrshire and Arran withheld the results of the internal inquiries - even from its own staff.
A nurse employed by the health board became concerned when he was involved in a critical incident, but never received a copy of the findings.
Rab Wilson was told he was not entitled to read the report, and would have to apply under FOI legislation.
When Mr Wilson did make an FOI request, he was told by the health board that the reports were exempt from disclosure because of patient confidentiality.
Realising that dozens of similar reports had also been withheld, Mr Wilson appealed to the information commissioner, who has now ordered the health board to release anonymised versions of the reports.
Mr Wilson told BBC Scotland: "These action plans and reports pertain to issues of patient safety, staff safety and were the worst events which happened there over the last five years - some really horrendous events.
"It appeared to me that the learning experience from these events was not being made available.
"I believe that in the new Scotland, which is a place of justice and fair play and compassion, workers should not be afraid to speak out - especially about serious, serious issues like this that impinge on patient safety, patient care and staff safety as well."
Information Commissioner Kevin Dunion said there had been a "catalogue of failings" by the board which may have been the most serious breach of FOI laws he had ever dealt with.
Mr Dunion added: "Claims made to Mr Wilson turned out to be wrong and prior assurances given to me and my staff turned out to be unjustified. At the very least, this constitutes a significant failure of records management, but, given the nature of the information which was the subject of the request, the failings may point to wider governance issues which have to be addressed.
"Mr Wilson's persistence was characterised by the board as being vexatious, but perhaps instead should have raised concerns that records concerning critical incidents which should have been held were missing, policies regarding action plans were not being adhered to and public confidence that plans had been drawn up and acted upon could be affected.
"Certainly I found it so difficult to believe that such documents could be unaccounted for in terms of whether they had been created, acted upon or destroyed, that it caused me to continue with my investigation despite the board's protestations."
Pillar to post
The health board's chief executive, John Burns, insisted it had not been attempting to suppress the critical incident reports, and said staff would now get copies of them.
He said: "We weren't burying reports. I think what the report highlights was that our systems back in 2006 weren't what they should have been.
"The reports were going out to managers, they were going out to be actioned but what we didn't have was a proper closure in the system back to evidence that the actions and the learning had been taken from those reports, and that's not right - we needed to have that."
Scottish Labour MP for Kilmarnock and Loudoun, Cathy Jamieson, said: "This is a welcome decision from Kevin Dunion, and it highlights a number of serious issues within NHS Ayrshire and Arran which must be addressed.
"I hope that the new chief executive will ensure that lessons are learned, and that Mr Wilson receives an apology for the way he has been treated."
She added: "He was put in a very difficult position as an employee of the health board, and at times it looked as though he was being thrown from pillar to post, when all he wanted was to help improve the service for patients."
Ms Jamieson called on the Scottish government's health secretary to ensure that the policy on Critical and Adverse incidents was adhered to in future.
Conservative MSP for Ayr, John Scott, called for a "full inquiry".
He said: "I am greatly concerned about the management failure of NHS Ayrshire and Arran highlighted in the freedom of information commissioner's report.
"More importantly, the opportunity to act on and improve the level of service to the public may have been lost as mistakes may have not been learned from because these action plans have not been made available to relevant staff."
Liberal Democrat health spokeswoman Alison McInnes also voiced concerns.
She said: "This is an astonishing lapse and raises grave questions over the handling of freedom of information requests at this health board."
Ms McInnes added: "The health secretary should now reassure us that every health board in Scotland has proper and robust reporting practices so situations like this can be avoided at all costs."