Background/Objectives: Adverse childhood experiences (ACEs) impact social, emotional, psychological, and physical development, often leading to health risk behaviors in adulthood. Instruments like the Adverse Childhood Experiences International Questionnaire (ACE-IQ) are essential for assessing ACEs globally and confirming their association with health outcomes in adulthood. Methods: This study evaluates the ACE-IQ's validity in a Chilean cohort by analyzing the prevalence of ACEs and the instrument's psychometric properties. Structural validity, internal consistency, and concurrent validity were assessed using the Marshall Scale as a comparative measure. Additionally, binary and frequency scoring methods were compared. Results: Structural validity analyses showed the best fit for three- and four-dimensional models using frequency scoring. The overall internal consistency of the scale was adequate (alpha > 0.7), although dimensions such as childhood neglect and violence outside the home demonstrated lower internal consistency. Concurrent validity showed significant positive correlations between ACE-IQ scores (both binary and frequency methods) and the Marshall Scale. Conclusions: The ACE-IQ demonstrates adequate reliability for the full scale, with strong evidence of construct validity using the frequency scoring method and concurrent validity for both scoring methods. These findings support the ACE-IQ's use for measuring childhood adversities in Chile and assessing their association with adult health outcomes.