On February 9, 2010, Lehtonen was traded to the Dallas Stars in exchange for Ivan Vishnevskiy and a fourth-round draft pick in the 2010 NHL Entry Draft (Ivan Telegin). Prior to the start of the 2010–11 season, the Stars signed Lehtonen to a three-year, $10.65 million extension. In his first full season in Dallas, Lehtonen compiled a 34–24 record with a 2.55 GAA. Lehtonen and the Stars were officially eliminated from contention for a seed in the 2011 playoffs after losing to the Minnesota Wild on the final day of the regular season.