Using family systems theory (Kerr & Bowen, 1988), interpersonal theory (Kiesler, 1996; Leary, 1957), and the interactional theory of countertransference (CT; Gelso & Hayes, 2007) as a framework, we investigated the influences of therapist personal factors (differentiation of self in relation to the family of origin; DoS) and client presentation as predictors of CT feelings and behaviors in response to a video analog client. Therapist-participants viewed either an interpersonally hostile-submissive or interpersonally hostile-dominant (HD) client. Overall, therapists lower in DoS reported significantly more overinvolved CT behaviors, overinvolved feelings, and underinvolved feelings compared with those higher in DoS regardless of client analog condition. Participants in the hostile-submissive condition reported significantly more overinvolved CT behaviors than those in the HD condition, whereas those in the HD condition reported more underinvolved CT feelings and behaviors than those in the hostile-submissive condition. Implications for theory and training are discussed. (PsycINFO Database Record (c) 2019 APA, all rights reserved)