Background One of the difficulties in assessing and treating PTSD in people with intellectual disability is that it may not present with the typical symptoms associated with the disorder. This may be why there is a dearth of literature on the treatment of PTSD using cognitive behavioural approaches for people with intellectual disability (e.g. Ehlers et al. Behav Res Ther, 43, 2005, 413–431). This paper reports the treatment for PTSD in a young man diagnosed with autism and a mild intellectual disability. Method Treatment involved 12 sessions of cognitive therapy for PTSD using the approach developed by Ehlers et al. Results There was an overall reduction in symptoms and a self‐reported elevation in mood. With careful questioning, adaptation of language and elucidation of concepts, the patient was able to fully engage in therapy. Discussion This case suggests that cognitive approaches to treating PTSD can be successful in people with intellectual disability and autism.