Background: Talking therapy for people with intellectual disabilities is often specifically adapted. One adaptation is the involvement of significant others in therapy, however, there is no systematic description of the use of this adaptation in routine clinical practice. Method: An online survey of UK psychologists regarding the inclusion of significant others in individual therapy with people with intellectual disabilities. Data were analysed using qualitative content analysis. Results: Ninety-five psychologists who work with people with intellectual disabilities provided responses to questions regarding the decision to include significant others in therapy, factors that make including significant others more or less likely and how the role of significant others is explained to them. Conclusions: Psychologists consider a range of factors in deciding the involvement of significant others. We discuss implications for training of therapists working with people with intellectual disabilities, issues of consent and how the roles of significant others are understood.