The 2004 Arizona Diamondbacks looked to improve on their 84–78 record from 2003. The D-backs hoped to contend for a postseason berth in what was a weaker National League West Division than in years past. However, just three years after winning a World Series title, the Diamondbacks instead finished the season with a record of 51–111, the worst record by any National League team since the 1965 Mets won one fewer game. The one highlight of a disastrous season was when Randy Johnson pitched a perfect game on May 18, 2004. The franchise record would not be threatened until 2021, when they finished 52–110. Despite the 110-loss season in 2021, the Diamondbacks didn't earn the first overall pick in the 2022 MLB Draft, as the Baltimore Orioles finished with a 52–110 record, but were worse due to records against American League opponents.
Offseason
November 28, 2003: Curt Schilling was traded by the Diamondbacks to the Boston Red Sox for Casey Fossum, Brandon Lyon, Jorge de la Rosa, and Michael Goss (minors). November 29, 2003: Jesse Orosco was signed as a free agent with the Diamondbacks. December 1, 2003: Lyle Overbay, Chris Capuano, Craig Counsell, Chad Moeller, Jorge de la Rosa, and Junior Spivey were traded by the Diamondbacks to the Milwaukee Brewers for Richie Sexson, Shane Nance and a player to be named later. The Brewers completed the deal by sending Noochie Varner (minors) to the Diamondbacks on December 15. December 4, 2003: Félix José was signed as a free agent by the Diamondbacks. December 15, 2003: Quinton McCracken was traded by the Diamondbacks to the Seattle Mariners for Greg Colbrunn and cash. December 18, 2003: Brent Mayne was signed as a free agent by the Diamondbacks. February 25, 2004: Bobby Estalella was signed as a free agent by the Diamondbacks. February 25, 2004: Scott Service was signed as a free agent by the Diamondbacks.
Regular season
Opening Day lineup
Season standings
National League West
Record vs. opponents
Notable transactions
June 11, 2004: Quinton McCracken was signed as a free agent by the Diamondbacks. July 31, 2004: Steve Finley and Brent Mayne were traded by the Diamondbacks to the Los Angeles Dodgers in exchange for Reggie Abercrombie (minors), Koyie Hill and Bill Murphy. August 19, 2004: Elmer Dessens was traded by the Diamondbacks to the Los Angeles Dodgers in exchange for Jereme Milons (minors).
Roster
Player stats
Batting
Starters by position
Note: Pos = Position; G = Games played; AB = At bats; H = Hits; Avg. = Batting average; HR = Home runs; RBI = Runs batted in
Other batters
Note: G = Games played; AB = At bats; H = Hits; Avg. = Batting average; HR = Home runs; RBI = Runs batted in
Pitching
Starting pitchers
Note: G = Games pitched; GS = Games started; IP = Innings pitched; W = Wins; L = Losses; ERA = Earned run average; SO = Strikeouts
Other pitchers
Note: G = Games pitched; IP = Innings pitched; W = Wins; L = Losses; ERA = Earned run average; SO = Strikeouts
Relief pitchers
Note: G = Games pitched; W = Wins; L = Losses; SV = Saves; ERA = Earned run average; SO = Strikeouts