He was drafted with the 2nd overall pick by the Atlanta Thrashers in the 2002 NHL Entry Draft. This made him the highest drafted European goaltender and highest Finnish player ever in NHL history. Lehtonen played 4 seasons with the Thrashers before he was traded to the Dallas Stars in exchange for Ivan Vishnevskiy and a 4th round draft pick (Ivan Telegin) on February 9, 2010.