In 1998, Kile signed with the Colorado Rockies as a free agent. Kile suffered control problems, allowing hitters to lay off his curveball. After two seasons in which he was a combined 21–30 and posted ERAs of 5.20 and 6.61, Kile was traded to the Cardinals. In his first season with St. Louis, Kile went 20–9, becoming the first Cardinal pitcher since John Tudor and Joaquín Andújar in 1985 to win 20 games in a season. He made his third All-Star team and again finished fifth in NL Cy Young Award voting. He earned the first playoff victory of his career in Game 2 of the 2000 NLDS against Atlanta, but suffered two losses in the NL Championship Series, which the Cardinals lost to the Mets in five games.