Psychological inflexibility (PI) refers to the overarching and nonadaptive avoidance of thoughts and feelings. PI is a transdiagnostic process that is present in numerous psychopathologies, such as anxiety and mood disorders, addictive behaviors, and chronic pain, as presented by American adults and adolescents. Despite the high rates of depression and depressed mood among Spanish and Latino adolescents and the observed relation between PI and adjustment problems at this age, an instrument assessing PI in Spanish-speaking adolescents is lacking. In this study, we assessed the psychometric properties of a Spanish adaptation of the Avoidance and Fusion Questionnaire for Youth with 483 students from Spain (mean age 13.89 years). The Spanish Avoidance and Fusion Questionnaire for Youth proved to be a two-factor psychometrically sound instrument. Total PI scores correlated positively with depression and negatively with satisfaction with life. The predictive validity results showed cognitive fusion and experiential avoidance to be two interrelated but distinct processes that characterize PI.