Terms weren't announced by the team, but the Los Angeles Times reported it's a four-year deal worth $57.4 million that will keep the seven-foot big man with the club through the 2012-13 campaign.
"We're extremely happy to have signed Andrew to this extension, which will secure his immediate future with the franchise," said Lakers general manager Mitch Kupchak. "Andrew has shown a vast array of skills for a player his size and if he continues to stay dedicated and work hard to improve, he has an excellent chance to develop into one of the top players in the NBA."
If an agreement had not been reached, Bynum would have become a restricted free agent next July; however, the Lakers would have had the right to match any offer he received from other teams.
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Bynum is playing in his fourth campaign in the NBA. He has averaged 10 points and six rebounds in LA's first two games this season. He played just 35 games in 2007-08 because of a left knee injury.
The 21-year-old Bynum, who had knee surgery during the offseason, has played in 165 games, with 80 starts, during his career. He owns career averages of 7.2 points and 5.6 boards per contest. Bynum has shot 56.9 percent from the floor and 64.9 percent from the charity stripe in the NBA.
The Lakers opened 2008-09 with convincing victories over the Portland Trail Blazers and the Los Angeles Clippers.
"This has been a fantastic week for me so far: turning 21, winning our first two games of the season, and now getting this new contract signed," said Bynum. "This gives me and my family financial security, and more importantly, cements my future with the Lakers, which in my opinion is the best organization in all of professional sports. I couldn't be happier."