Background: The aims of the current study were to adapt a version of the MET for people with intellectual disabilities and assess its ecological and construct validity. Material and Methods: Using a correlational design, 40 participants with intellectual disabilities were invited to complete a battery of neuropsychological assessments and the modified Multiple Errands Test for Intellectual Disabilities (mMET-IDs). Results: The ability to successfully complete tasks on the mMET-IDs correlated significantly with measures of the Supervisory Attentional System, namely, the Tower of London Test and the Six Parts Test. However, performance on the mMET-IDs and the Six Parts Test could be accounted for by Verbal IQ and receptive vocabulary. The mMET-IDs failed to correlate with the DEX-IR. Conclusions: The mMET-IDs can be successfully used to assess some aspects of the Supervisory Attentional System in people with intellectual disabilities. Further development is needed, however, to improve the ecological validity of the mMET-IDs.