TUCSON, Ariz. -- Arizona coach Lute Olson has retired after 25 years with the Wildcats.
"This was not a decision that was made lightly," Olson said in statement. "I've had a wonderful run at The University of Arizona. I leave with a great sense of pride in what we have accomplished here."
Speaking at a brief news conference at McKale Center, Arizona athletic director Jim Livengood did not designate a successor -- even on an interim basis. He said a national search would begin soon.
"I do not have a decision at this point in time in terms of who's going to head our men's basketball program," Livengood said. "But that will be announced in the very, very short future."
ESPN's Dick Vitale first reported the story, saying Olson would be replaced by assistant coach Mike Dunlap, a former Denver Nuggets assistant and Metro State coach who joined the program in May.
"At this stage in my life, I want to devote my time to my children, grandchildren, great-grandchildren, family and friends," Olson said. "I look forward to watching Wildcat basketball and visiting with my colleagues in the coaching profession. It is time to pass the program on to a younger staff, to transition the university to the next generation of basketball."
Olson missed all of last season after taking a personal leave of absence for what he later termed "a medical condition that was not life-threatening."
Interim coach Kevin O'Neill led Arizona to a 19-15 record and the school's 24th consecutive NCAA tournament appearance, the nation's longest active streak.
When Olson returned from his leave in April, he said O'Neill was no longer part of his staff and that he planned to coach for the remainder of his contract, which runs through 2011.
On Tuesday, Olson said that he was fired up about the upcoming season. "I feel much more energized at this point," he said at the team's media day.
That feeling apparently changed quickly. Olson skipped a scheduled luncheon on Wednesday and missed practice the last two days.
Olson did not appear at the news conference announcing his decision, nor was there any mention of his health in the statement released by the school.
The announcement comes after a year of upheaval for Olson, whose contentious divorce from wife Christine was finalized last spring. Five months later, Olson announced that he was engaged to Kelly Pugnea, 47, a Tucson resident for 25 years.
Last month, the university reported a possible minor NCAA recruiting violation by Olson, who called it "an unfortunate and regrettable error."
Olson went 589-187 at Arizona, and he led the Wildcats to the 1997 national title and four Final Fours, most recently in 2001. His 327 Pac-10 wins are a conference record.
Olson is 780-280 overall as a Division I coach.
As rumors of Olson's retirement spread, television news trucks lined the street outside McKale Center. Reporters camped out inside the building for hours as Livengood and other school officials huddled in the athletic department offices, refusing to confirm or deny widespread reports that Olson had quit.
"This has been a long day for everybody," Livengood said. "Things were released, unfortunately, non-confirmed, a long time ago, and it seems like it's been hours and hours and hours."
Olson's decision sent shockwaves across a basketball-obsessed campus. Football coach Mike Stoops was swarmed by reporters after practice, and none wanted to ask about Arizona's Homecoming game against No. 6 USC, which pits two teams tied for first in the Pac-10.
"He's an icon," said Stoops, who first met Olson when Stoops was a football player at Iowa. "I just hope and pray he's in good health and happy with his decision. He deserves it. He's put a lot of time and energy into building a tradition here, second to no other across the country."
Olson was the coach for one season at Long Beach State before he took over at Iowa for the 1974-75 season.
He was inducted into the Naismith Memorial Hall of Fame in 2002.
ESPN.com's Andy Katz and The Associated Press contributed to this report.