Pit the cherries. If desired, drain accumulated juices into a liquid measuring cup. Add enough water to reach 2/3 cup.
Combine water (or water/juice) and sugar in a small saucepan. Bring to a boil, stirring to dissolve sugar. Continue cooking until a thin syrup forms.
Add the cherries and stir for 1 minute. If you want to keep the cherries whole, remove from heat now. Alternately, continue cooking over medium for about 5 minutes, until cherries are more broken down.
Pour into a jar or airtight container and cool to room temperature, then cover and chill until ready to use.
Notes
Makes about 1 pint.
Adapted from The Complete Book of Small-Batch Preserving.