The government has denied forcing the head of the NHS in England, Sir Nigel Crisp, to stand down because of financial problems in the service.
Sir Nigel took up post in 2000
Downing Street denied Sir Nigel was "carrying the can" as the NHS headed towards a record overspend for 2005-6.
The Conservatives said the departure was "a clear admission" of crisis.
Sir Nigel, 54, who has been chief executive since November 2000, has overseen huge spending increases and waiting list falls to record lows.
Looking back over the past five years, Sir Nigel said he was proud the NHS had achieved or exceeded the challenging targets it had been set.
He added: "There've been enormous changes but not everything has gone well. I am particularly saddened by the financial problems we're grappling with.
"As chief executive I wish to acknowledge my accountability for these problems, just as I may take some credit for the achievements."
He said the timing of his retirement "was right" for the health service, adding: "The NHS needs a chief executive who can give leadership over several more years."
NHS managers have reported that operations are being delayed and wards closed as they struggle to balance the books.
The government predicted a possible deficit of £620 million back in December, but no one really knows what the figure will be at the end of the financial year.
Many health trusts have cut posts or brought in recruitment freezes.
And many lay the blame for the financial mess at the door of the government and its officials.
The government says spending has only outstripped resources in a quarter of trusts and that 'turnaround teams' are helping them bring finances out of the red.
Downing Street denied Sir Nigel was "carrying the can" for NHS cash problems, saying taking responsibility was part of leadership.
A spokesman added that Sir Nigel had been granted a peerage, on the personal recommendation of Prime Minister Tony Blair.
'NHS in chaos'
Health Secretary Patricia Hewitt commended Sir Nigel's achievements in driving through "huge improvements" in patient care.
However shadow health secretary Andrew Lansley said Sir Nigel's rushed departure was "a clear admission" the NHS was in crisis.
"Ministers can try and blame Sir Nigel but they are responsible.
"The NHS is plunging into the red because ministers raised costs and pushed targets without regard to the overall impact on services."
Following Sir Nigel's departure, the NHS chief executive's job will be split.
Sir Ian Carruthers, who is the Department of Health's acting director of commissioning, takes over as acting NHS chief executive.
Hugh Taylor, the director of strategy and business development, becomes acting permanent secretary.
Liberal Democrat health spokesman Steve Webb supported the move to split his the roles into head of the NHS and permanent secretary.
He said the NHS needed a boss who could sometimes tell the government that the policy being pursued was damaging the health service.
Dr Gill Morgan, chief executive of the NHS Confederation which represents over 90% of NHS bodies, said Sir Nigel had overseen a turbulent period of record change which, when complete, would transform the NHS into a 21st Century organisation.
James Johnson, British Medical Association chairman, said there were clearly problems in the NHS and that he looked forward to working with Sir Nigel's successors to help tackle these problems in the best way.