Background: To assess epistemic trust in people with intellectual disabilities, we adapted the Questionnaire Epistemic Trust (QET) for people with mild to moderate intellectual disabilities or borderline intellectual functioning (MMID/BIF). Method: We investigated the factor structure, the reliability and construct validity in 147 adults. Results: We replicated the 4-factor structure, after excluding four items with low factor loadings. Internal consistency was [alpha] = 0.58 for Hypervigilance, and ranged from a = 0.74 to 0.81 for the other subscales. Subscale test-retest reliability ranged from 0.504 to 0.747. No convergent validity was found with the Reflective Functioning Questionnaire (RFQ). Discriminant validity was confirmed with the Scale of Emotional Development-Questionnaire (SED-Q), Scale of Emotional Development-Short (SED-S) and Autism Spectrum Quotient-10 (AQ-10), but not with General Social Trust (GST). Discussion: The QET is promising for assessing epistemic trust of people with MMID/BIF at subscale level. Refining the items with a figurative expression seems needed.