Background: Attachment theory predicts that the quality of early care shapes the development and consolidation of later mental representations of attachment, which in turn influence mental health. Attachment representations are increasingly operationalized as secure base script knowledge—one’s level of awareness of the temporal-causal schema that summarizes the basic features of seeking and receiving effective support from caregivers when in distress. Though a recent method was developed to assess secure base script knowledge during the Adult Attachment Interview (AAI _sbs), its predictive validity on mental health outcomes is largely unknown. Method: In a series of pre-registered analyses, we leveraged two relatively large, longitudinal cohorts - the normative-risk NICHD Study of Early Child Care and Youth Development ( N = 857) and the higher-risk Minnesota Longitudinal Study of Risk and Adaptation ( N = 178) - to assess the associations between AAI _sbs in late adolescence and depression in adulthood, and compare these associations to traditional attachment representation measures. Results: Higher AAI _sbs in normative-, but not higher-risk adolescents, predicted fewer depressive symptoms in adulthood, above and beyond concurrent depressive symptoms, sociodemographic and cognitive functioning covariates, and other traditional attachment representation measures. Across both normative- and high-risk samples, AAI _sbs did not significantly differ from other attachment representation measures in the strength of their respective associations with adulthood depression. Conclusions: Findings point to the predictive significance of AAI _sbs for mental health in normative-risk adolescents, supporting the importance of considering expectations regarding seeking and receiving effective support from caregivers at times of need in developing interventions to improve adolescent well-being.