The broad personality trait of disinhibition reflects the tendency to behave in an underconstrained versus overconstrained manner and is associated with externalizing psychopathology and risk-taking behaviors. This article describes the development and initial validation of the Disinhibition Inventory (DIS-I), a multifaceted measure of disinhibition that helps explicate the nature of this important higher-order dimension more fully. Factor analyses of an initial item pool resulted in five content-distinct, yet correlated scales measuring both high (Manipulativeness, Distractibility, Risk Taking) and low (Prosociality, Orderliness) levels of disinhibition that cross-validated in an independent sample. Evidence for the construct validity of the DIS-I is presented, including convergent and discriminant relations with Big-Three and Big-Five/five-factor model measures of personality. Results indicate that the DIS-I scales are associated most strongly with other measures of disinhibition, but that the DIS-I additionally contains content absent in extant adult measures of disinhibition that may prove useful in the assessment of externalizing psychopathology. (Contains 7 tables and 6 notes.)