Lee was traded to the Cubs for Hee-seop Choi.
He hit .278 with 32 home runs and 98 RBIs in his first year with the Cubs.
In 2005, Lee had a career first half of the season, with an MLB-leading .376 batting average, 72 RBIs, and a tie for the major league lead in home runs with 27.

The Cubs had traded superstar Sammy Sosa, who had previously been one of their best hitters, before the 2005 season.
Lee showed early on that he could more than compensate for the loss, and while Sosa had a disappointing 2005 season with the Baltimore Orioles, Lee had a career year.
By midseason, he was among MLB's leaders in each of the triple crown categories: batting average, home runs, and RBIs.
Lee hit his 200th career home run on August 28, 2005, off Florida Marlins starter Josh Beckett.
He finished the year with a career-best 46 home runs.
His .335 batting average was the highest by a Cub since Bill Madlock's .339 in 1976 and made him the first Cub since Bill Buckner in 1980 to win a National League batting title.
He also finished third in NL MVP voting and won the NL Gold Glove and Silver Slugger awards at first base that year.

Lee was named to the U.S. roster for the 2006 World Baseball Classic, where he was the first player to hit a home run for Team USA in the World Baseball Classic.

On April 10, 2006, Lee signed a five-year, $65 million extension with the Chicago Cubs.
The deal replaced his contract for the 2006 season and extended him as the Cubs' first baseman through the 2010 season and included a no-trade clause.
He broke his wrist less than two weeks later, in a collision involving baserunner Rafael Furcal, and he missed 59 games due to the injury.
The Cubs posted a 19–40 record during Lee's stint on the disabled list.
Later, Lee went back on the disabled list with a post-traumatic inflammation in the outer bone of the medial side of the wrist.

In 2008, Lee hit 20 home runs, 90 RBIs and had a .291 batting average as the Cubs had the best regular-season record in the National League, leading the Cubs to the NL Central championship, later losing in the NLDS to the Los Angeles Dodgers, 3-0.
In 2009,  Lee overcame a slow start with a 21 game hitting streak from May 29 until June 24 and finished ninth in the voting for NL MVP, as he had a .306 batting average, and hit for 35 home runs and 111 RBIs.

On June 9, 2010, Lee hit his 300th career home run in a game against the Milwaukee Brewers.

On June 25, 2010, Lee was involved in a dugout altercation with Cubs pitcher Carlos Zambrano after the pitcher gave up four runs in the first inning and apparently blamed Lee for failing to field a sharply-hit lead-off double.
Zambrano was suspended for his behavior.
Lee was traded to the Cubs for Hee-seop Choi. He hit .278 with 32 home runs and 98 RBIs in his first year with the Cubs. In 2005, Lee had a career first half of the season, with an MLB-leading .376 batting average, 72 RBIs, and a tie for the major league lead in home runs with 27.
The Cubs had traded superstar Sammy Sosa, who had previously been one of their best hitters, before the 2005 season. Lee showed early on that he could more than compensate for the loss, and while Sosa had a disappointing 2005 season with the Baltimore Orioles, Lee had a career year. By midseason, he was among MLB's leaders in each of the triple crown categories: batting average, home runs, and RBIs. Lee hit his 200th career home run on August 28, 2005, off Florida Marlins starter Josh Beckett. He finished the year with a career-best 46 home runs. His .335 batting average was the highest by a Cub since Bill Madlock's .339 in 1976 and made him the first Cub since Bill Buckner in 1980 to win a National League batting title. He also finished third in NL MVP voting and won the NL Gold Glove and Silver Slugger awards at first base that year.
Lee was named to the U.S. roster for the 2006 World Baseball Classic, where he was the first player to hit a home run for Team USA in the World Baseball Classic.
On April 10, 2006, Lee signed a five-year, $65 million extension with the Chicago Cubs. The deal replaced his contract for the 2006 season and extended him as the Cubs' first baseman through the 2010 season and included a no-trade clause. He broke his wrist less than two weeks later, in a collision involving baserunner Rafael Furcal, and he missed 59 games due to the injury. The Cubs posted a 19–40 record during Lee's stint on the disabled list. Later, Lee went back on the disabled list with a post-traumatic inflammation in the outer bone of the medial side of the wrist.
In 2008, Lee hit 20 home runs, 90 RBIs and had a .291 batting average as the Cubs had the best regular-season record in the National League, leading the Cubs to the NL Central championship, later losing in the NLDS to the Los Angeles Dodgers, 3-0. In 2009,  Lee overcame a slow start with a 21 game hitting streak from May 29 until June 24 and finished ninth in the voting for NL MVP, as he had a .306 batting average, and hit for 35 home runs and 111 RBIs.
On June 9, 2010, Lee hit his 300th career home run in a game against the Milwaukee Brewers.
On June 25, 2010, Lee was involved in a dugout altercation with Cubs pitcher Carlos Zambrano after the pitcher gave up four runs in the first inning and apparently blamed Lee for failing to field a sharply-hit lead-off double. Zambrano was suspended for his behavior.
Derrek Lee