Bush served as the 41st US president from 1989 to 1993.
His chief of staff Jean Becker said: "President Bush is in the hospital. We have kept this quiet out of respect for him."
Bush has been in and out of hospital, and was most recently admitted the day after Thanksgiving.
He was visited there Sunday by his son, former US president George W. Bush and daughter-in-law Laura Bush.
"His big problem is a chronic cough he can't get rid of, so he's back at Methodist," Becker said. "This is not a life-threatening illness."
Becker said there were some earlier concerns that the cough would turn into pneumonia, but it has not.
Bush is expected to be discharged this weekend, she added.