Background: This study explored the effectiveness of eye movement desensitisation and reprocessing (EMDR) therapy for post-traumatic stress disorder (PTSD) in persons with mild to borderline intellectual disability (MBID) using a multiple baseline across subjects design. Methods: One child and one adolescent with MBID, who met diagnostic criteria for PTSD according to a PTSD clinical interview (i.e., ADIS-C PTSD section), adapted and validated for this target group, were offered four sessions of EMDR. PTSD symptoms were measured before, during and after EMDR, and at six weeks follow-up. Results: For both participants, number of PTSD symptoms decreased in response to treatment and both no longer met PTSD criteria at post-treatment. This result was maintained at 6-week follow-up. Conclusions: The results of this study add further support to the notion that EMDR can be an effective treatment for PTSD in children and adolescents with MBID. Replication of this study in larger samples and using a randomized controlled design is warranted.