["Social Development, Volume 35, Issue 3, August 2026. ", "\nABSTRACT\nAdolescence is a period when interpersonal distrust and perceived social isolation become significant risk factors for adverse psychosocial outcomes. However, there is limited longitudinal evidence quantifying the relative importance of early‐life antecedents of these risk factors. Using the UK's Millennium Cohort Study, we conducted an exploratory, hypothesis‐generating analysis of early‐life factors associated with distrust and social isolation at 14 years (11,069 participants, 51% female, 20% non‐White, 44% in disadvantaged areas at study‐entry). Predictors included child, family, and environmental factors from perinatal and early childhood periods. Exploratory random forest analyses were used to rank‐order 28 theoretically motivated predictors and to prioritise those most strongly associated with each outcome. Survey‐weighted multiple regression models were then used for descriptive follow‐up analyses to characterise shared and distinct antecedents of distrust and social isolation. Distrust and social isolation at age 14 were weakly correlated (r=0.32,p<0.001$(r = 0.32,p < 0.001$). Exploratory regression analyses indicated that a shared antecedent was callous–unemotional traits (standardised β=0.10$\\beta = 0.10$ for distrust and β=0.13$\\beta = 0.13$ for social isolation, with p<0.001$p < 0.001$ for both). Female sex, lower household income, and hyperactivity/inattention predicted distrust but not social isolation, whereas poorer interparental relationship quality and special educational needs were distinct antecedents of social isolation but not distrust. The findings of this study uncover both shared and distinct early‐life antecedents of adolescent distrust and perceived social isolation. Implications for practitioners with a prevention‐oriented approach include the need to target interparental relationship quality in the perinatal period, hyperactivity/inattention problems in early childhood, and callous‐unemotional traits.\n"]