The purpose of this paper was to further establish the validity of the Autism Spectrum Disorder-Diagnostic for Children (ASD-DC). The methodology consisted of testing the similarity of findings between the ASD-DC and the Autism Diagnostic Interview-Revised (ADI-R), which proved to be statistically significant for subscale content scores on social, communication, and rituals/insistence on sameness/restrictive interest subfactors. Secondly, the ASD-DC and ADI-R were compared to clinically derived diagnoses based on diagnostic interviews, rating scales, a DSM-IV/ICD-10 symptom checklist, observations of the child, clinical judgment, and an in-depth parent interview. Twenty-six children in the study met criteria for ASD while six did not. The ASD-DC correctly identified 73% of the ASD group and 67% of the controls, while the ADI-R correctly identified 46% of the ASD group and 100% of the controls. The implications of these data are discussed. (Contains 3 tables.)