This study examined the role of adolescents’ perceived close relationships with significant others (attachment relationships with mothers/fathers, appraisal of homeroom teacher as secure base, and quality of peer friendship) in explaining differences in their socioemotional and behavioral functioning (peer-network/peer-dyadic loneliness, positive/negative affect, and externalizing/internalizing problems), among adolescents with learning disabilities (LD), with comorbid LD and attention-deficit/hyperactivity disorder (ADHD), or with typical development (TD). Participants were 280 adolescents in Grades 10 through 11 in three groups: LD (n = 90), comorbid LD and ADHD (n = 91), and TD (n = 98). Preliminary analyses yielded significant group differences on most socioemotional and behavioral measures. Structural equation modeling (SEM) analysis indicated high fit between the theoretical model and empirical findings and partially different patterns of relationships among the model’s components for the three populations. The discussion focuses on the possible unique value of close relationships with each significant attachment figure for adolescents with LD, comorbid LD–ADHD, and TD.