Background: Individuals with intellectual disability respond differently to traumatic events, compared to the general population, which makes post-traumatic stress disorder (PTSD) symptoms difficult to recognize. The current study aims to examine the presence of undetected PTSD among individuals with intellectual disability and a known history of trauma exposure. Method: Nine individuals, who have not previously been diagnosed with PTSD, were evaluated for PTSD symptoms through case reports, which include descriptions of medical history, symptoms and behavior described in the former diagnostic reports, potential traumatic experiences, current symptoms and behavior in accordance to the Lancaster and North Gate Trauma Scale, and PTSD criteria from DM-ID. Results: Four out of the nine participants met the DM-ID criteria for PTSD. Conclusions: The current findings highlight the importance of including cognitive impairment and developmental level in the screening, referral and treatment process of PTSD.