This paper describes the development of protocols with interpreters employed in an East London psychological trauma clinic. The service treats traumatized refugee people with cognitive methods, according to the National Institute for Clinical Excellence (NICE) Guidelines for PTSD. NICE states that language should not be a barrier to treatment, but provides no further guidance to achieve this. These protocols for interpreting CBT are designed to be explicit, consistent and ethical. A telephone poll from a recent UK-wide trauma survey, a focus group with local interpreters, and practitioner reflection were all used to develop and refine the protocols and their rationale, which are described, together with implications for future culturally sensitive practice and research.