In a saucepan combine grapefruit juice, sugar, and cinnamon.
Bring to boiling; reduce heat. Simmer, uncovered, for 5 minutes.
Discard cinnamon; cool syrup. Cover and chill syrup.
Fill four 8-ounce glasses with ice.
Add about 1/3 cup grapefruit syrup to each glass.
Fill glasses with ginger ale. Stir gently.
Recipe from the Juice Products Association