Welsh health minister Edwina Hart has denied opposition claims she misled the Assembly about the existence of a report into the NHS.
Opposition AMs have previously called for Mrs Hart to release the findings, but were told there was no such report and that no “formal document for scrutiny” was available.
But Mrs Williams attacked the assembly government after obtaining a leaked document into the financial stability of the NHS, marked “restricted” and “draft”.
Under the heading “shortcomings we have heard”, it says that strategic objectives are “too numerous and not prioritised, so none or the wrong ones are implemented”.
It adds that “implementation lacks accountability” and that “initiatives are financially unaffordable”.
Mrs Williams said: “This Government must take responsibility for its failures and it is wholly unacceptable that Assembly members and the people of Wales have been misled by the health minister to protect herself.”
An Assembly Government spokesman said: “The minister has not misled anyone. There is no McKinsey report.
“The NHS chief executive and health boards commissioned work on developing a Five-Year Service, Workforce and Financial Framework to take forward the NHS reforms.
“This exercise included, at various stages, numerous inputs and analysis, some of which was provided by McKinsey. The document that Kirsty Williams is referring to is one such example.
“The minister has been transparent throughout the whole process.”
He said that, far from denying the issues facing the NHS, a five-year plan published in May “clearly highlights the challenges” the service must confront.