["Family Relations, EarlyView. ", "\nAbstract\n\nObjective\nThe primary goals of the present study were to (a) differentiate types of adolescents' attachment‐related insecurity with their custodial grandmothers and (b) examine associations, including bidirectional relations, between grandchildren's attachment insecurity and their maladjustment symptoms 9 months later.\n\n\nBackground\nThere is limited research on attachment‐related insecurity for adolescents in the care of custodial grandparents—a group that may be at heightened risk for insecure relationships and poor adjustment symptoms.\n\n\nMethods\nAdolescent grandchildren (n = 348; aged 11 to 18 years, 39.7% male) reported on the quality of their relationship with their custodial grandmother and their internalizing and externalizing symptoms at T1 and T2 (9 months later). Bifactor analyses were used to compute orthogonal indices of attachment‐related general insecurity, anxious‐ambivalence, and avoidance.\n\n\nResults\nWithin time, general insecurity predicted higher internalizing and externalizing symptoms. T1 general insecurity longitudinally predicted higher T2 externalizing and internalizing symptoms, with relations for externalizing symptoms moderated by length of care. Interestingly, T1 internalizing symptoms positively predicted T2 general insecurity.\n\n\nConclusions\nConsistent with attachment theory and prior research on parent–child relationships, grandchildren's relationship quality with their custodial grandmother predicted later maladjustment symptoms.\n\n\nImplications\nFindings highlight the importance of attending to grandchildren's attachment‐related insecurity in providing supportive services and resources to custodial grandfamilies.\n\n"]