Bush, the 41st U.S. president, fell on Wednesday at his summer home in Kennebunkport but was doing OK, a Bush spokesman said.
"41 fell at home in Maine today and broke a bone in his neck," spokesman Jim McGrath tweeted on Wednesday night. "His condition is stable -- he is fine -- but he'll be in a neck brace."
Bush was being treated at Portland's Maine Medical Center, where a children's hospital is named for his wife. The medical centre confirmed his condition was stable but said it was premature to speculate about when he'll be released. It said he would be there at least overnight.
Bush, who has a form of Parkinson's disease and uses a motorized scooter or a wheelchair for mobility, has suffered other recent health setbacks.
He was hospitalized in Houston in December for about a week for shortness of breath. He spent Christmas 2012 in intensive care at the same Houston hospital for a bronchitis-related cough and other issues.
Bush, a Republican, served two terms as Ronald Reagan's vice-president before being elected president in 1988. After one term, highlighted by the success of the 1991 Gulf War in Kuwait, he lost to Democrat Bill Clinton amid voters' concerns about the economy.
Bush, the father of Republican former President George W. Bush, was a naval aviator in World War II and was shot down over the Pacific. He also was a former U.S. ambassador to China and a CIA director.
He has skydived on at least three of his birthdays since leaving the White House. He celebrated his 90th birthday by making a tandem parachute jump near his Kennebunkport home. He celebrated a low-key 91st birthday with his family there.
During the winter, Bush and his wife, Barbara Bush, live in Houston.
Another Bush son, Republican former Florida Gov. Jeb Bush, is running for president in 2016.Suggest a correction