OBJECTIVES: Prolonged grief disorder (PGD) is a debilitating condition recently recognized to psychiatric diagnostic manuals. There is a pressing need for valid, reliable, and culturally adapted instruments that align with internationally established diagnostic criteria for the diagnosis of pathological grief, particularly for Latinx populations, who often face limited access to timely mental health services. This study aimed to translate, adapt, and validate the Mexican version of the PG-13-R scale. METHODS: We translated and then back-translated the original PG-13-R. The scale was reviewed by experts in psychometrics and cognitively debriefed with a Mexican sample. The study included 397 participants, consisting of: (1) Family members of patients who died from cancer and received supportive care from a patient navigation program at a public hospital in Mexico City (CDMX) and (2) Individuals from the broader community who were contacted via social media (X, Facebook). Participants completed an online survey that included sociodemographic data, the preliminary version of the PG-13-R, an assessment of depression (PHQ-9) and of anxiety (GAD-7). Internal consistency was analyzed using Cronbach's alpha. A confirmatory factor analysis (CFA) was conducted to examine evidence of validity, along with a Pearson correlation analysis between PG-13-R scores and existing measures assessing related but distinct constructs (i.e., depression and anxiety). RESULTS: CFA supported a 1-factor structure with good model fit after accounting for error covariance between related items. The Mexican PG-13-R demonstrated good internal consistency (Cronbach's α = 0.89) and positive significant correlations with measures of depression and anxiety, providing evidence of score reliability and validity. SIGNIFICANCE OF RESULTS: The adapted PG-13-R offers a culturally appropriate tool for assessing prolonged grief in Mexican Spanish-speaking populations, with potential for use in clinical and research settings. The use of the PG-13-R scale is recommended for clinical research and mental health care in the Mexican population.