George Alagiah, 58, has been diagnosed with bowel cancer.
"He is grateful for all the good wishes he has received thus far and is optimistic for a positive outcome," a statement from the BBC said.
"George asks that he and his family are given the space and privacy they require whilst he recovers."
The presenter of the BBC news at Six and Ten, as well as GMT on BBC World News, is set to take a break from television while he undergoes treatment.
The BBC confirmed that the news programmes would be presented by “familiar faces... until such time as George is well enough to return to work”.
"Our thoughts are with him and his family and we send them our very best wishes during this time," the statement continued.
Alagiah joined the BBC in 1989 as one of the broadcasting house’s leading foreign correspondents. He later moved into presenting and was made an OBE in the 2008 New Year’s Honours.