Objective: In psychotherapy clients' I don't know-responses (IDK-responses) to therapists' questions are typically considered to be non-cooperating behaviors. How therapists actually handle these behaviors remains unclear. This study therefore aims to assess client-therapist interactions following IDK-responses. Methods: Data were collected in a Dutch child and adolescent mental healthcare service by observing Dialectical Behavior Therapy aimed at adolescents with severe emotional distress. Eighteen individual psychotherapy sessions involving two therapists with six clients were video-recorded and transcribed. Stand-alone IDK-responses were selected (n = 77) and analyzed using conversation analysis. Results: Adolescents' IDK-responses led to varying actions of therapists. We identified five categories of continuations after IDK-responses: no IDK-related continuation; redoing of the question; proposing a candidate answer; employing therapy-specific techniques; and meta-talk on the problematic nature of the IDK-response. Conclusions: Therapists treat IDK-responses not just as non-cooperative behavior on the part of the client; IDK-responses are also used as a starting point to collaboratively enhance clients' insights in their own thoughts, emotions, and behaviors. Practice implications: After IDK-responses therapists can use a variety of continuation strategies with varying therapeutic functions. These strategies can be embedded in training of therapists to deal with potentially non-cooperative behavior. (C) 2016 Elsevier Ireland Ltd. All rights reserved.