The present study aimed to identify intergenerational patterns of attachment insecurity among grandmothers, adolescent grandchildren, and birth mothers in custodial grandfamilies and to test the relations among triadic attachment patterns and grandchild socioemotional outcomes. Prior research with custodial grandfamilies has found distinct "profiles" reflecting patterns of closeness between grandmothers, grandchildren, and birth mothers. However, no studies have tested patterns of attachment insecurity among members of the triad, despite the likelihood of attachment disruption in grandfamilies. Moreover, previous studies have only examined links between profile and grandmother outcomes or rudimentary grandchild outcomes. In a sample of 230 grandmother-grandchild dyads from a larger randomized controlled trial testing the efficacy of an online social intelligence training program for grandfamilies, latent profile analysis (LPA) was conducted to identify profiles of intergenerational attachment insecurity, using grandmother and grandchild reports. Profile differences in grandchild internalizing and externalizing problems, social skills, self-esteem, and prosocial behavior were examined. We identified three profiles: isolated mother, grandchild-linked, and disconnected. Overall, grandchildren in disconnected families (in which attachment insecurity between all three members of the triad was high) fared worst. Grandchildren in isolated mother families (in which only grandmother-grandchild attachment insecurity was low) fared best. A secure attachment relationship between grandmother and adolescent grandchild may buffer effects of attachment insecurity between the grandchild and birth mother. These findings inform intervention efforts and highlight the utility of family- and attachment-focused research for building understanding of custodial grandfamilies. (PsycInfo Database Record (c) 2023 APA, all rights reserved).