The 2003 League of Ireland First Division season was the 19th season of the League of Ireland First Division and the first to be played as a summer league.
The First Division was contested by 12 teams and Dublin City won the division. Each team played the other teams three times, totaling 33 games.
Four teams entered the promotion/relegation play-off. The second, third and fourth placed teams from the First Division were joined by the ninth placed team from the 2003 League of Ireland Premier Division.
Derry City win 4âÂÂ0 on aggregate
Finn Harps win 3âÂÂ1 on aggregate
Derry City win 2âÂÂ1 on aggregate and retain their place in the Premier Division.