Cabrera was signed by the Baltimore Orioles as an amateur in 1999. He did not become a player in the Orioles minor league system until 2000, at the age of 19. For his first two seasons as a minor leaguer, Cabrera played in the rookie leagues; first with the Gulf Coast Orioles,then with Bluefield. He posted a 5.49 ERA his first season and a 3.28 ERA his second. When he was 22, Cabrera became a part of the Orioles Single-A ballclub, the Delmarva Shorebirds. His record was 5–9 with a 4.24 ERA. By the end of his third season in the minors, Cabrera was racking up the numbers one would expect from a power pitcher. He recorded 105 strikeouts over 101 innings of work with the rookie leagues between 2001 and 2002, and added 120 strikeouts over 125.1 innings in Single-A Delmarva the following season. He was promoted to Double-A Bowie before the 2004 season. While at Bowie, Cabrera began dominating; through five starts, he posted a 2.39 ERA and averaged over 11 strikeouts per nine innings. On May 11, 2004, he was called up to make his major league debut against the Chicago White Sox. Cabrera did not disappoint. In his very first start against the Atlanta Braves, he tossed six shutout innings. In June, he had a 2.83 ERA and held opponents to a mere .204 batting average. Though utterly dominating for the first few months, Cabrera's control slowly left him; by the end of the season, he was walking far too many batters to be effective, and finished the season with an even 5.00 ERA. He finished third in AL Rookie of the Year voting. At the start of the 2005 season, Cabrera was listed as the Orioles #2 starter, thanks to a dominating Grapefruit League performance. His performance was extremely up-and-down, however. Though he had many utterly dominating performances, he had an equal number of disastrous outings. His 2005 ERA of 4.52 belies the inconsistency he experienced from start to start. During 2005, Cabrera's name surfaced in trade rumors involving A. J. Burnett of the Florida Marlins. These trade rumors never reached fruition, however, and Burnett and Cabrera both remained with their respective teams for the duration of the season. Cabrera once again demonstrated his potential in 2006 with some dominating performances against major-league caliber rosters while pitching in the WBC. Many baseball experts, including ESPN analysts Rob Neyer and Peter Gammons, predicted a breakout season for Cabrera in 2006. However, on July 14, 2006, Cabrera, after showing inconsistency at the major league level (leading the majors in both walks (75) and wild pitches (13)), was optioned to Triple-A Ottawa. To take his place in the starting rotation, left-hander Adam Loewen was recalled from Ottawa. Cabrera was recalled on August 7, 2006, and pitched a complete game shutout against the Toronto Blue Jays on August 19, 2006, allowing only five hits. On September 28, 2006, Cabrera took a no-hitter into the 9th inning against the New York Yankees before surrendering a line drive single to Robinson Canó. He completed the game, only giving up that one hit. Cabrera was the losing pitcher for the Orioles on August 22, 2007. That day, the Orioles suffered the worst beating in baseball since 1897, blowing a 3-run lead and losing to the Texas Rangers 30–3. Cabrera was ejected in the fourth inning for throwing a beanball at the head of the Boston Red Sox's second baseman, Dustin Pedroia on September 7, 2007, after a third base balk. MLB commentators have cited this as being another instance of Cabrera being a man of massive potential with poor major league career execution. On September 13, 2007, he was suspended six games by Major League Baseball for the incident. In 2007, he had the lowest range factor of all major league pitchers, 0.75. In 2008, Cabrera was 5–1 with a 3.48 ERA through 10 starts, but fell off after that. He finished the year leading the majors in hit batters (18) and had the majors' worst strikeout:walk ratio (1.06), and led the American League in wild pitches (15), and finished second in the AL with 90 walks. Overall, he finished the season 8–10 with a 5.25 ERA. On December 12, the Orioles gave up on Cabrera and did not tender him a contract.