This study gathers evidence of the validity of a translated and Spanish-adapted version of the International Trauma Questionnaire (ITQ) evaluating both post-traumatic stress disorder (PTSD) and complex post-traumatic stress disorder (CPTSD) in a clinical sample of Mexican women exposed to traumatic experiences. ITQ and a measure of traumatic events were administered to a purposive sample of 112 adult Mexican women attending an outpatient psychiatric service. The psychometric properties of the ITQ were evaluated according to the guidelines of the International Test Commission. The items were analyzed using G-theory, reliability analysis, and exploratory and confirmatory factor analysis. The instrument showed to have validity and reliability in this population, with adequate generalization and dependence coefficients (G theory), appropriate reliability indices, and a factorial structure congruent with the original theory. 55% of the participants classified with CPTSD and 14% with PTSD. The ITQ is a brief screening instrument that adequately distinguishes between PTSD and CPTSD in a clinical sample of Mexican women and may help make fundamental decisions in terms of treatment. Further analysis of the psychometric properties of this scale is recommended.