Interpreting is increasingly being used in psychotherapy, but the presence of an interpreter in the therapeutic encounter is an under-researched area. This paper examines interpreter-mediated trauma therapy with Danish-speaking therapists treating Arabic-speaking patients diagnosed with post-traumatic stress disorder (PTSD). We focus on the notion of ‘emotion discourse’ as a broad term covering how therapists and patients talk about emotional experience, and how interpreters negotiate and mediate it. The data consist of three group interviews with ten therapists and six excerpts from two audio-recorded interpreter-mediated therapy sessions. The detailed interaction analysis explores (1) the therapists’ expectations about interpreting emotion discourse and (2) the interactional strategies that the interpreters use to negotiate and render the interaction between therapists and patients who speak different languages. The findings show that the therapists have clear expectations about what needs to be translated and how, but these expectations remain hidden to the interpreters. The interpreters use various interpreting strategies and orient towards meaning rather than towards verbatim translations. We conclude by recommending that both therapists and interpreters engage in a professional collaboration that requires not only training and awareness of mutually relevant information, but also an updated view of interpreter-mediated interaction as a dynamic collaborative process.