Madelyn Dunham, 86, raised Obama during his teenage years in Hawaii, while his mother was living in Indonesia. The campaign said she is gravely ill in Honolulu, The New York Times reported.
"I think everyone understands that the decision that Senator Obama is making to go to Hawaii underscores the seriousness of the situation," campaign spokesman Robert Gibbs said. "As he has said, she poured everything she had into him."
The campaign has canceled events in Des Moines, Iowa, and Madison, Wis. Obama will make an unexpected stop in Indianapolis on Thursday since that stop aligns with his plan to depart for Hawaii, Gibbs said.
Obama is expected to return to the campaign trail Saturday. He takes a break at a time when he leads Republican John McCain in all the national polls.