Specialist investigators have been called in to Betsi Cadwaladr University Health Board after auditors discovered at least £122m was allegedly not properly accounted for.
Audit Wales is also conducting a “high level review of board effectiveness” to understand what went wrong and how.
The Welsh government said it was unable to comment on an active investigation.
Issues were first uncovered earlier in the year when auditors found a number of “significant errors” in the health board’s account for the 2021-22 financial year.
They allegedly found there was £72m of unpaid invoices and bills listed in the accounts, but could not find evidence that they existed.
Overall, auditors are said to have raised concerns that £122m of expenditure was not properly accounted for. The Welsh financial watchdog, Audit Wales, said it was still investigating to work out whether and how the money was spent.
Accountancy and consulting firm EY were commissioned to review the accounts after auditors raised concerns. Following their report, the NHS Counter Fraud Service Wales was asked to investigate. The NHS Counter Fraud Service is an independent body which looks into allegations which can include economic crime in the NHS, including fraud, bribery and corruption.
BBC Wales understands none of the issues being investigated involve anyone making personal gain.
This scandal does not seem to be about corruption but about incompetence … 