There has been an increased interest in the structure of and relations among executive functions.The present study examined the factor structure as well as age-related factorial invariance of the Delis-Kaplan Executive Function System (D-KEFS), a widely used inventory aimed at assessing executive functions. Analyses were first conducted using data provided in the D-KEFS technical manual and were then replicated in an independent sample of male early adolescents aged 11 to 16 years. Results revealed a three-factor solution best fit the data across groups and samples; measurement properties appeared to be invariant across age groups for certain loadings and variant for others. The three factors were labeled Conceptual Flexibility, Monitoring, and Inhibition. These findings provide better understanding of the measurement properties of the D-KEFS and contribute to the larger literature on the structure of measures intended to assess executive functions. (Contains 2 notes and 9 tables.)