Rehnquist was treated at Bethesda Naval Hospital (search) in suburban Maryland. He is expected to be back at the court on Nov. 1, court officials said Monday.
The news of Rehnquist's health briefly stunned even the political campaigns.
"I think this is our time to let his family and friends know that our thoughts and prayers are with them," said Bush campaign communications director Nicole Devenish.
Rehnquist, 80, joined the court in 1972, having been appointed the previous year by President Nixon (search) and confirmed by the Senate despite strong objections from Democrats.
He was made chief of the court by President Reagan in 1986 to replace retiring Chief Justice Warren Burger. Rehnquist is the second-oldest chief justice. First was Roger Taney, who presided over the high court in the mid-1800s until his death at 87.
Rehnquist is one of the nine justices who is frequently cited as a possible retiree in the coming presidential term. If he or another justice does leave the bench, the next president will be faced with the first nomination since 1994, when then-President Bill Clinton appointed Stephen Breyer (search) to fill the seat vacated when Justice Harry Blackmun retired.
Rehnquist served in the Army Air Corps in North Africa during World War II. He has three degrees from Stanford and one from Harvard University. He also served as an assistant attorney general for the office of legal counsel under John Mitchell, Nixon's attorney general. In that role as the president's counsel, he helped develop a legal justification for the invasion of Cambodia and for the application of warrant-less wiretaps.
He is considered a reliable force on the Supreme Court for conservatives, though he is not the most conservative member on the bench. However, he has voted in a conservative manner on most issues from school desegregation to granting additional police powers. He has favored the rights of states to make law rather than the force of federal law, though his support for law-and-order issues has sometimes interfered with his support for states' rights.
"He has a keen legal mind. He, of course, is a pillar of the conservative side of the court. But it is important to understand that when we speak about conservative in this sense, we mean that he is a great believer in separation of powers, he believes in judicial restraint, he believes in states' rights as opposed to what we referred to back in the '60s and '70s when we were speaking largely of individual rights," said Barry Richard, a trial attorney who petitioned the court for President Bush in the 2000 presidential recount case.
"He is one of the legal giants of our time. Agree with him or not, no one over the recent decades has had more influence on our laws than William Rehnquist, and I think historians will some day look back on the Rehnquist court and conclude he would be on the short list of Americans who have had the most influence on the shaping of this country's history over the last 34 years," former U.S. Attorney Kendall Coffey told FOX News.
This is not the first time the chief justice has fallen ill. In November 2002, Rehnquist was admitted to a hospital to undergo knee surgery following an injury from a fall at his home. In 1995, doctors removed a herniated disc in Rehnquist's lower back.
Other members of the high court have also been treated for cancer. Justice John Paul Stevens, the oldest at 84, has had prostate cancer. Justice Sandra Day O'Connor had breast cancer and Justice Ruth Bader Ginsburg had colon cancer.
Rehnquist's scheduled return to the court means he will be involved in potential legal challenges stemming from the election next week. Already, the court has had to deal with several legal issues related to this election season, including a decision Saturday to leave independent presidential candidate Ralph Nader off the ballot in Pennsylvania. The high court has not yet acted on a similar appeal from Nader involving Ohio.
FOX News' Anna Persky and James Rosen and The Associated Press contributed to this report.