Evidence for the validity of the Behavior Rating Inventory of Executive Function (BRIEF; Gioia, Isquith, Guy, & Kenworthy, 2000) based on internal structure was examined in a sample of children with mixed clinical diagnoses via maximum likelihood confirmatory factor analysis. Four alternative factor models of children's executive function, based on current theories that posit a unidimensional versus fractionated model (Rabbitt, 1997; Shallice & Burgess, 1991), using the revised 9-scale BRIEF configuration that separates two components of the Monitor scale, were examined for model fit. A 3-factor structure best modeled the data when compared directly with 1-, 2-, and 4-factor models. The 3-factor model was defined by a Behavior Regulation factor consisting of the BRIEF Inhibit and Self-Monitor scales, an Emotional Regulation factor consisting of the Emotional Control and Shift scales, and a Metacognition factor composed of the Working Memory, Initiate, Plan/Organize, Organization of Materials, and Task-Monitor scales. The findings support a fractionated, multi-component view of executive function as measured by the BRIEF.