Abstract Aims The International Trauma Questionnaire (ITQ) is a novel assessment instrument that is aligned to the ICD‐11 diagnoses of post‐traumatic stress disorder (PTSD) and complex PTSD (CPTSD). The purpose of this study was to develop and evaluate an adapted version of the ITQ suitable for use by people with intellectual disabilities. Methods The ITQ‐ID follows the original ITQ, using wording developed in collaboration with a focus group of people with intellectual disabilities The ITQ‐ID was administered to 40 people with intellectual disabilities recruited from learning disability forensic and community settings, alongside a Trauma Information Form and the Impact of Event Scale‐Intellectual Disabilities (IES‐IDs). Results Most participants reported multiple traumatizing events. Around half of the participants met strict criteria for a diagnosis of PTSD, and around three quarters met looser criteria. Depending on definitions, between 66% and 93% of those who met criteria for PTSD also met criteria for a diagnosis of CPTSD. The ITQ‐ID showed a single‐component structure, with very good‐to‐excellent internal consistency, excellent test–retest reliability, and evidence of concurrent, discriminant, and content validity. Significance The results support the potential of the ITQ‐ID for assessment of PTSD and CPTSD in people with intellectual disabilities in both clinical and research contexts and highlight the need for further validation work.