Background: Little is known about the efficacy of eye movement desensitization and reprocessing (EMDR) therapy for post-traumatic stress disorder (PTSD) symptoms in people with mild intellectual disability or borderline intellectual functioning (MID-BIF). Aims: To explore the safety, feasibility, and efficacy of EMDR therapy in adults with MID-BIF, PTSD, and comorbid mental health and psycho-social problems. Methods and procedures: Data were collected from nine participants using a non-concurrent multiple baseline design. PTSD symptoms, level of daily life impairment, and possible adverse effect were measured weekly during baseline, treatment, post-treatment, and at three-month follow-up. Depressive symptoms, general psychopathology, and mental health problems were assessed once in every phase. Outcomes and results: Participants displayed a significant reduction of PTSD symptoms, and the majority of participants no longer met criteria for DSM-5 PTSD diagnosis after therapy. EMDR therapy appeared to be safe, as no adverse events were reported during the study time frame. Further, participants showed a decrease in depressive symptoms as well as less severe general psychopathology and mental health problems following therapy. Conclusion: EMDR therapy was found to be safe, feasible, and (potentially) efficacious in decreasing PTSD symptoms, loss of PTSD diagnoses, reduction of level of daily life impairment, and general psychopathology for adults with MID-BIF, suffering from both severe mental health and psycho-social problems.