The woman in charge of mental health services in Brighton and Hove and across Sussex is being treated at a Brighton hospital for inflammation of the gall bladder.
Sussex Partnership NHS Foundation Trust said that its chief executive Lisa Rodrigues had had acute cholecystitis diagnosed.
She is being treated at the Royal Sussex County Hospital in Brighton.
John Bacon, chairman of Sussex Partnership, said: “Lisa Rodrigues, our chief executive, is currently on sick leave awaiting gall bladder surgery.
“Sue Morris, executive director of corporate services, will serve as acting chief executive until Lisa’s return.
“We all wish Lisa a prompt recovery.”