In a small saucepan, bring the sugar and water to a boil. Reduce heat and simmer about 7 minutes. Stir to dissolve sugar. Remove from heat and let cool completely.
While the simple syrup is cooling, strain freshly squeezed lemon and lime juice into a resealable bottle or jar, discarding the pulp and seeds. Pour in the cooled simple syrup. Shake and use immediately or refrigerate.