The aim of this study was to gain an in-depth understanding of psychotherapists’ experiences of working with adult clients with a diagnosis of Asperger Syndrome/High Functioning Autism (AS/HFA). People with AS/HFA are very susceptible to developing mental health issues, most notably depression and anxiety. With a greater awareness of AS/HFA in recent years and increasing rates of diagnosis, more adults with AS/HFA are now presenting for psychotherapy. However, to-date there appears to be no qualitative research exploring the experiences of psychotherapists who work with this client group. Thus, the current Interpretative Phenomenological Analysis (IPA) study aimed to address this gap in the literature by interviewing nine therapists who work with adult clients with a diagnosis of AS/HFA. Analysis of the data identified three superordinate themes: (1) “Being in a One-Sided Relationship”, captures the participants’ feeling that they were in a one-sided or non-reciprocal relationship, (2) “Feeling Frustrated and Inadequate”, reflects the participants’ frustration and their sense of inadequacy experienced when working with this client group, and (3) “Needing to Adapt”, captures the participants’ experiences of adapting their approach and/or suppressing part of themselves in order to accommodate their AS/HFA clients and prevent them from dropping out of the therapy. The novel findings to arise from the current study were the therapists’ difficulty reading their AS/HFA clients, their desire or need to experience empathy back from the clients, their experiencing of self-doubt, and their need to adapt when working with these clients. These findings are discussed in relation to existing literature and their potential implications for policy, practice, training and research are explored. A number of conclusions were drawn from the current findings, most notably that more evidence-based AS/HFA-specific training be provided for psychotherapists.Abstract