Combine sugar and flour in top of double boiler; gradually stir in milk. Cook over medium heat about 5 minutes, stirring constantly until thickened.
Beat egg yolks until thick and lemon colored. Gradually stir about 1/2 of hot mixture into yolks; add to remaining hot mixture, stirring constantly. Cook over medium heat, stirring constantly about 2 minutes or until thickened. Remove from heat, and stir in pineapple. Let cool.