Stephen Day has spent less then 18 months in the post

Stephen Day's departure came without warning on Friday. A hospital spokesman said it was a personal matter and not something he could discuss.

Mr Day, 50, was appointed to run the trust and the newly-opened hospital in September 2002 and began the job in January 2003.

A short statement from the trust thanked him for his commitment and wished him well in the future.

Mr Day, formerly chief executive of Broadland NHS Primary Care Trust, said he was delighted when he was appointed to succeed Malcolm Stamp who left to become chief executive at Addenbrooke's NHS Trust, Cambridge.

He joined the NHS in 1972 and has held a range of positions, including regional director of finance at the West Midlands Health Authority, and regional director of the NHS Executive, West Midlands.

The trust board has yet to appoint a successor to Mr Day.