Barbara Bush, the wife of former US President George HW Bush, is in "failing health" and has decided to no longer seek medical treatment, the office of the ex-president has said in a statement.
The statement said the former first lady "will instead focus on comfort care."
Mrs Bush is 92-years-old.
The short statement did not indicate the nature of Mrs Bush's illness but said that she had had a series of recent hospitalisations.
US media reported that she was suffering from chronic obstructive pulmonary disease (COPD) and congestive heart failure, and is being cared for at home.
As first lady from 1989 until the start of 1993, Mrs Bush was a popular national figure known for her sometimes blunt talk and self-deprecating wit.
"She is surrounded by a family she adores and appreciates the many kind messages and especially the prayers she is receiving," the statement added.
Mrs Bush is the mother of former President George W Bush, 71, the 43rd US president.
Her husband, the 41st US president, is 93-years-old.
Another son, Jeb, is a former governor of Florida who ran unsuccessfully for president in 2015 and early 2016, quitting after a series of lackluster performances highlighted by tough skirmishes with then-candidate Donald Trump.
With hair that had turned white prematurely, Mrs Bush was known by family members as the "Silver Fox".
Her work as first lady focused on promoting literacy and reading.
At the time, she said she was more interested in running a household than in helping her husband run the country.
Mrs Bush holds a unique place in US history as she is the only woman to see her husband and son sworn in as US president.