The Externalizing Spectrum Inventory (ESI; Krueger, Markon, Patrick, Benning, & Kramer, 2007) provides a self-report based method for indexing a range of correlated problem behaviors and traits in the domain of deficient impulse control. The ESI organizes lower order behaviors and traits of this kind around higher order factors encompassing general disinhibitory proneness, callous-aggression, and substance abuse. In the current study, we used data from a male prisoner sample (N = 235) to evaluate the validity of ESI total and factor scores in relation to external criterion measures consisting of externalizing disorder symptoms (including child and adult antisocial deviance and substance-related problems) assessed via diagnostic interviews, personality traits assessed with self-reports, and psychopathic features as assessed with both interviews and self-reports. Results provide evidence for the validity of the ESI measurement model and point to its potential usefulness as a referent for research on the neurobiological correlates and etiological bases of externalizing proneness.