Introduction: The aim of this study is to validate a Spanish version of the Impact of Event Scale on People with ID (IES-ID). Methods: IES-ID was administered to adults with ID (n = 120), analyzing internal consistency, inter-rater and test-retest reliability, criterion validity, construct validity and feasibility. Results: Good internal consistency was found in the total of the scale ([alpha] = 0.91). Test-retest and inter-rater correlations yielded excellent level of agreement in the total scale. Criterion validity was significant. Regarding construct validity, the factor analysis yielded three well-defined factors and the model fit of the confirmatory factor analysis appears to be very good. Finally, the feasibility was also very good. Conclusion: The Spanish version of the Impact of Event Scale for People with ID (IES-ID) showed adequate indexes of feasibility and reliability to assess the severity of PTSD symptoms in adults with borderline to moderate ID.