Background: There is a lack of research on trauma in people with intellectual disabilities. This study assessed expert consensus on the traumatic potential of a broader range of adverse life events, and differences in symptom manifestation and behavioural symptom equivalents of post-traumatic stress disorder (PTSD) symptoms. Method: The present authors conducted a three-step Delphi survey using a mixed-methods design. Twenty-nine expert raters participated in the survey, and 16 persisted to the final round. Consensus was calculated using the interquartile range. Results: Traumatic potential was attributed to adverse life events, particularly revolving around sexuality and autonomy. DSM-5 symptoms of PTSD were rated as partially adequate, with behavioural symptom expression being the main difference to the general population. Conclusion: The range of traumatic events should be broadened for people with intellectual disabilities. A specific subset of events need to be defined in future research. Detection of PTSD depends upon determining specific symptom correlates of challenging behaviour.