Background: There is established evidence of complicated grief among people with an intellectual disability. This paper describes the process of adapting complicated grief therapy (CGT) for this population. Method: Action research documented the adaptation of CGT. Qualitative methods included analysing meeting notes, reflective interviews with two members of the team involved in adapting the materials, and interviews with six professionals working in disability settings who reviewed the adapted materials. Results: Key processes included adapting the standardised tools that form part of CGT and developing adapted approaches to abstract concepts related to death, dying and bereavement. Key therapeutic components such as imaginal revisiting and the role of significant others required adaptation for implementation with people with intellectual disabilities. Conclusion: The importance of adapting evidence-based therapies for people with intellectual disabilities is emphasised. This research provides an adapted form of an established therapy for piloting with this population.