This study examined the degree to which the parent-child relationship uniquely predicted clinical outcomes in externalizing problems and adaptive skills in children meeting diagnostic criteria for oppositional defiant disorder and whether facets of this relationship moderated the effects of two unique psychosocial treatments. We recruited 134 children and their parents (38.06% female; M age = 9.52 years, range = 7-14; 83.58% White). Families were randomly assigned to 1 of 2 treatments: Parent Management Training (PMT) and Collaborative and Proactive Solutions (CPS). We formed principal components from pretreatment reports and behaviors of the parent-child relationship to predict within- and between-family outcomes in children's externalizing problems and adaptive skills. Four principal components were supported (parental warmth, parental monitoring, family hostility, and family permissiveness). Parental monitoring predicted fewer externalizing problems, whereas family permissiveness predicted more externalizing problems. Parental warmth predicted greatest improvements in children's adaptive skills among families receiving PMT. Family hostility predicted more externalizing problems and poorer adaptive skills for children; however, families receiving CPS were buffered from the negative effect of family hostility on adaptive skills. The parent-child relationship can uniquely inform posttreatment outcomes following treatment for oppositional defiant disorder. Certain treatment approaches may better fit unique relationships that emphasize warmth and/or hostility, allowing clinicians to anticipate and tailor treatments to families.