Horn was the 1982 first round draft pick (16th Pick) of the Boston Red Sox. In 1987, after batting .321, with 30 home runs, 82 runs batted in (RBI’s) and a league leading .649 slugging percentage for the Triple-A level Pawtucket Red Sox, Horn was called up to the Boston Red Sox mid-season. He continued to find success, hitting .278 with 14 home runs and 34 RBI’s in just 158 at-bats as a rookie with the major league Red Sox. During his eight-season major league career with Boston, Baltimore, Cleveland, and Texas, Horn hit .240, with a total of 62 home runs, including 23 home runs during the 1991 season as a member of the Baltimore Orioles. After leaving MLB, Horn played for the Taipei Gida in 1997 and 1998. He hit the first home run in the Taiwan Major League and held the record of being the highest paid player in the Taiwan professional baseball history (USD $216,000 for the 1997 season) until surpassed by Chin-Feng Chen in 2006.