Achieving expertise in psychotherapy is a complex task, fraught with obstacles that impede progress (e.g., cognitive and information processing, accuracy of self-appraisals; Tracey, Wampold, Lichtenberg, & Goodyear, 2014). Contrary to popular opinion, years of experience does not make for an expert therapist. Research indicates that more seasoned therapists are not necessarily more effective than less seasoned therapists in terms of client outcomes. Expertise requires not only time, but also an intention to improve; and the use of appropriate feedback systems. Certain therapist characteristics can reliably predict therapy process and outcome. For example, the degree to which therapists feel uncertain regarding their ability to help clients, known as self-doubt, is a particularly strong predictor of client outcomes (Nissen-Lie, Monsen, Ulleberg, & Rønnestad, 2013). Currently, little is known about therapists’ self-doubt regarding clients’ different presenting problems. There is qualitative evidence that therapists experience the greatest self-doubt in response to clients who are, subjectively, described as high-stakes, unmotivated, violent, aggressive, suicidal, and intensely emotional (Thériault & Gazzola, 2010). Among disorders that manifest these characteristics, conduct disorder (CD) in adolescence is the most representative. This is the first, known study which examined the relation between client characteristics and the expression of self-doubt among therapist trainees in the United States. Participants in the current study read and responded to four vignettes portraying scenarios of adolescent boys with mental illness, in a within-subjects design. Self-doubt was assessed after each vignette using a measure constructed and validated for developing therapists (Orlinsky & Rønnestad, 2005). Ancillary measures assessed participants’ interpersonal reactivity (i.e., perspective taking, empathic concern) as well as their sense of self-efficacy in various counseling behaviors (i.e., session management, counseling challenges). Therapist trainees expressed greatest PSD when working with adolescent males who exhibit CD-Severe, followed by obsessive-compulsive disorder (OCD) and CD-Mild equally, and finally social anxiety disorder (SAD). Overall, clients with externalizing disorders elicit the greatest PSD among therapist trainees. This information may provide evidence for self-doubt as a target in therapist feedback systems in the quest to develop expertise in therapy