The chief executive of the NHS trust which runs Queen Alexandra Hospital in Portsmouth has left her post.
A statement from Portsmouth Hospitals NHS Trust said Ursula Ward, who had held the role for 12 years, had "taken the decision to leave".
No reason has been given for her departure.
The trust has recently faced criticism over delays in its emergency department, with patients kept waiting in ambulances outside the hospital.
A statement said: "The Board would like to thank Ursula for her valued contribution and dedication and wish her every success in the future."
Tim Powell, current director of workforce and organisational development, has been appointed interim chief executive.
Portsmouth North MP Penny Mordaunt paid tribute to Ms Ward's "hard work and effort".
"She was the first nursing director to become the CEO of a hospital and she has helped transform the QA, most notably in my book dramatically reducing infections," she said.
The hospital's emergency department was criticised in February when a third of Hampshire's on-duty fleet of 46 ambulances queued outside. The trust said it had been "exceptionally busy"