OBJECTIVE Although there are currently several efficacious treatments for depressed and suicidal adolescents, less is known about predictors and moderators of adolescents' treatment response. A growing literature has identified family functioning as a prognostic indicator of adolescents' likelihood of benefiting from treatment. The current study tested both observational and perceived measures of family functioning as indicators of adolescents' response to 2 treatment conditions. METHODS The sample consisted of 129 depressed and suicidal adolescents (Mage = 14.96, 82.9% female, 56% Black/African American) who were randomized to attachment-based family therapy or family-enhanced nondirective supportive therapy (Diamond et al., 2019). Baseline assessments of family functioning included ratings of parent-adolescent communication coded with the Goal-Corrected Partnership in Adolescence Coding System (Lyons-Ruth, Hennighausen, & Holmes, 2005) and adolescent and parent reports of Family Conflict and Cohesion from the Self-Report of Family Functioning (Bloom, 1985). RESULTS Adolescents who engaged in more uncooperative communication with their parents during a 10-min conflict discussion showed greater reductions in depressive symptoms in both treatments. Adolescents from traditionally underserved (non-White or lower income) families showed greater reductions in suicidal ideation in both treatments. CONCLUSIONS Attachment-based family therapy and family-enhanced nondirective supportive therapy were most effective for adolescents from traditionally underserved families and adolescents who engaged in less cooperative communication with their caregivers. Observational ratings of parent-adolescent communication were better prognostic indicators of treatment response than were self-reported indicators of global family functioning. Implications for generalizing these results to other treatments for depressed and suicidal adolescents are discussed. (PsycINFO Database Record (c) 2019 APA, all rights reserved).