In 1-quart saucepan, cook sugar and water over medium heat, stirring constantly, until sugar is dissolved. Remove from heat; cool to room temperature.
Stir in lemon juice. Store mixture in tightly covered nonmetal container or jar in refrigerator.
For each serving, in tall glass, mix 1/2 cup chilled mixture and 1/2 cup ginger ale. If desired, add ice.