Returning the trophy has no practical effect on Bush since he's already in the pros and a member of a Super Bowl championship team. However, it is the first time in the award's 75-year history that a player has forfeited it.
USC was hit with heavy sanctions by the NCAA this summer after it determined Bush and his family had received hundreds of thousands of dollars in gifts from two fledgling California-based marketing agents. The NCAA ruled that Bush was ineligible for the 2005 season, which opened the possibility that the Heisman Trophy Trust would take back the award.
One of the few guidelines given to Heisman Trophy voters is that a player must be in compliance with NCAA rules to be eligible for the award.
"The persistent media speculation regarding allegations dating back to my years at USC has been both painful and distracting," Bush said in a statement released through the Saints. "In no way should the storm around these allegations reflect in any way on the dignity of this award, nor on any other institutions or individuals.
"For the rest of my days, I will continue to strive to demonstrate through my actions and words that I was deserving of the confidence placed in me by the Heisman Trophy Trust."
Shortly after USC was sanctioned, the eight-member trust, based in New York, said it was considering what to do about Bush, who won in a landslide vote over Texas quarterback Vince Young.
The trust met Tuesday; it had no comment. Whether the 2005 Heisman will be vacated or given to Young remains to be seen.
"Reg will continue to be the 2005 Award recipient and I will continue to be honored to have been in the 2005 Heisman campaign with such a talented athlete," Young posted on his Twitter account.
Allegations of improper benefits to Bush and his family were first reported by Yahoo! Sports in September 2006, months after Bush had already been drafted No. 2 overall by the Saints.
The NCAA and Pac-10 began investigating him and the USC football program soon afterward, and Bush immediately denied any wrongdoing.
One of the marketing agents, Lloyd Lake, sued Bush in trying to recoup nearly $300,000 in cash and gifts. Eventually, the case was settled and Bush never had to publicly tell his side of the story.
In handing out its penalties, the NCAA cited USC for a lack of institutional control. Its report cited numerous improper benefits for Bush and former basketball player O.J. Mayo, who spent just one year with the Trojans.
The penalties included the loss of 30 football scholarships over three years and vacating 14 victories in which Bush played from December 2004 through the 2005 season. USC, under coach Pete Carroll, beat Oklahoma in the BCS title game on Jan. 4, 2005, and won 12 games during Bush's Heisman-winning season, which ended with a loss to Texas in the 2006 BCS title game.
After the 2009 season, Carroll left USC to take over as coach of the NFL's Seattle Seahawks.
"It is my hope that this situation serves as a teachable moment to all involved, especially for the young athletes and university and high school administrators of tomorrow," Carroll said in a statement.
In July, USC replaced athletic director Mike Garrett with Pat Haden, and one of the first moves Haden made was returning USC's copy of Bush's Heisman Trophy.
"It was a very noble thing for Reggie to do," Haden said. "In my opinion, he made the right decision. It was a thoughtful decision by Reggie.
"It's never a good thing to give a Heisman back. But at the end of the day, USC did the right thing when we gave our Heisman back and now Reggie did, too."
Bush's decision ends four years of questions, debate and turmoil surrounding allegations that tainted one of the great performances in college football history.
"It doesn't matter if he gives it back. Everyone still knows Reggie Bush was the best player that year. Look at the runs. He was clearly the best player," said Johnny Rodgers, 1972 Heisman winner from Nebraska. "O.J. Simpson got accused of a murder and they didn't take his back. That was a far greater allegation, and they didn't find O.J. guilty on that."
Former Nebraska quarterback Eric Crouch, who won the Heisman in 2001, called it a "sad day."
Eddie George, the 1995 Heisman winner from Ohio State, felt the same way: "I don't think he should've gave his Heisman away. I think it's a shame that it's come to this for Reggie."
USC won 34 straight games and two national titles during Bush's sensational three-year career.
In 2005, he was spectacular, running for 1,740 yards, scoring 18 touchdowns and helping the Trojans reach the national championship game against Texas and Young.
In winning the Heisman, Bush received 784 first-place votes, the third-most in the history of the award and finished 933 points ahead of Young.
But it was Young who came away with the biggest prize.
He scored the winning touchdown with 19 seconds left in Texas' 41-38 victory at the Rose Bowl. Bush's most memorable play from the title game was an ill-advised lateral that resulted in a USC turnover.
Bush jumped to the NFL as a junior after that bowl game and was drafted by the Saints.
As a pro, he's had some brilliant moments and has been a productive player. However, so far, he has fallen short of becoming the star he was projected to be.
"Now that this is behind me I look forward to the future and winning more awards and championships here in New Orleans! Who Dat!" Bush tweeted.
--- AP Sports Writers Eric Olson in Omaha, Neb., and Teresa Walker in Nashville, Tenn., contributed to this report.