As an off-shoot of a study examining the reliability and validity of an adapted version of the Pre-Linguistic Autism Diagnostic Observation Schedule (A-PL-ADOS), 13 individuals with Down syndrome with IQs ranging between 24 and 48 were administered the Autism Diagnostic Interview-Revised (ADI-R) and the A-PL-ADOS, which are well-validated interview and observational diagnostic measures. Three out of 13 met lifetime criteria on the ADI-R, but none of these three showed behavior that met the criterion for autism on the APL-ADOS (although two nearly did so). However, two individuals did meet the A-PL-ADOS criterion and showed behavior that fell only just short of meeting lifetime criteria on the ADI-R. Altogether, 5 individuals with Down syndrome may be considered to show an autism spectrum disorder. Of the remaining 8, some showed a few autistic features, and some showed none. The findings raise both methodological and conceptual issues.