In the current study, we examined a specific aspect of executive abilities, strategic processing, in 32 children with early-treated phenylketonuria (PKU) and 41 typically-developing control children. To do so, clustering and switching were assessed during semantic (animal, food/drink) and phonemic (S, F) fluency tasks. Specifically, number of words generated, number of subcategory clusters, number of words in subcategory clusters, and number of switches between subcategories were analyzed to provide a refined analysis of strategic processing. Compared with controls, children with PKU generated significantly fewer words and made significantly fewer switches between subcategories in the food/drink trial and the phonemic fluency condition. Number of switches was associated with number of words generated in these tasks. In addition, a significant interaction between age and group in number of switches for the food/drink trial reflected a greater increase in number of switches for the control than PKU group as a function of increasing age. These results suggest impairment in frontally-mediated aspects of strategic processing in children with early-treated PKU and indicate that strategic processing should be evaluated carefully as these children age.