Currently there are no available sleep disorder measures for individuals with severe and profound intellectual disability. We, therefore, attempted to establish the external validity of the Diagnostic Assessment for the Severely Handicapped-II (DASH-II) sleep subscale by comparing daily observational sleep data with the responses of direct care staff to the sleep subscale of the DASH-II. Participants included 25 individuals with severe intellectual disability and 25 individuals with profound intellectual disability who reside in a large developmental center in central Louisiana. Four of the five items of the DASH-II were shown to have external validity. Implications of these findings for future research and practice are discussed.