Background: Partnerships between mental health care stakeholders provide a context for generalizable clinical research with implications for quality improvement. In the context of a partnership between an adolescent residential substance abuse disorder (SUD) treatment center and clinical researchers, stakeholders identified knowledge gaps (internal and the field broadly) with regard to patient interpersonal factors that influence working alliance and acute SUD residential treatment outcome trajectories. Objective: To (a) examine interpersonal pathoplasticity and identify interpersonal subtypes in a naturalistic sample of adolescent and young-adult patients presenting for routine residential SUD treatment and (b) investigate the association between identified interpersonal subtypes and working alliance and acute treatment outcome trajectories. Method:N = 100 patients (Mage = 17.39 years, 68% male, 84% White) completed self-reports of symptom and functioning outcomes, interpersonal problems, and the working alliance on multiple occasions between admission and discharge. Multiple methods were used to identify interpersonal subtypes and test pathoplasticity. Interpersonal subtype was entered as a predictor in respective multilevel models of working alliance and symptom outcome. Results: Interpersonal subtypes of vindictive and exploitable patients demonstrated pathoplasticity. Subtype did not predict working alliance trajectories; however, a significant interaction between interpersonal subtype and a quadratic effect for time demonstrated that exploitable patients with longer than average treatment lengths experienced attenuated symptom change over the course of treatment whereas vindictive patients appeared to demonstrate steady progress. Conclusions: Interpersonal assessments should be integrated into residential SUD treatment to identify patients with an exploitable interpersonal style who might require additional attention or alternative interventions.