["Journal of Traumatic Stress, EarlyView. ", "\nAbstract\nAdverse childhood experiences (ACEs) are linked to numerous negative physical and mental health outcomes. The current study addressed theoretical, conceptual, and measurement problems by evaluating a novel extension to the seminal ACEs questionnaire (ACEs‐Q). Two U.K.‐based adult samples (NStudy 1 = 859, NStudy 2 = 297) were used to examine the structure of the ACEs‐Q via principal component analysis (PCA) and, within a structural equation modeling (SEM) framework, reflective and composite–formative models, as well as to develop and validate a supplementary measure—the ACEs‐Related Impairment Questionnaire (ACEs‐RIQ)—designed to assess the impairment associated with ACEs. In Study 1, PCA supported a two‐factor ACEs‐Q structure encompassing Childhood Maltreatment (CM) and Household Challenges (HC) factors. Both SEM approaches showed similar associations with internalizing outcomes, primarily driven by CM, composite–formative: βDepression = .50, βAnxiety = .43, βStress = .42; reflective: βDepression = .51, βAnxiety = .43, βStress = .42. Although the findings indicate compatibility of the ACEs construct with both modeling approaches, the composite–formative model, where dichotomous items function as contributing indicators that form rather than reflect the construct, is more closely aligned with the current conceptualization of ACEs. In Study 2, the ACEs‐RIQ demonstrated high internal consistency, Cronbach's α = .92, and predictive validity comparable to the ACEs‐Q, tested through SEM. The ACEs‐RIQ was found to be a valid, reliable instrument that extends the ACEs‐Q by capturing impairment due to adversity rather than exposure alone.\n"]