The smallest subset of items from the 30-item Checklist for Autism Spectrum Disorder (CASD) that differentiated 607 referred children (3–17 years) with and without autism with 100% accuracy was identified. This 6-item subset (CASD-Short Form) was cross-validated on an independent sample of 397 referred children (1–18 years) with and without autism and on data from 1417 children in the CASD standardization sample and 1052 children in the CASD normative sample, resulting in 98.5, 97.6, and 99.8% diagnostic accuracy, respectively. Diagnostic agreement was high between the CASD-Short Form and the Autism Diagnostic Interview-Revised (96%), and the Child Autism Rating Scale (98%). Diagnostic accuracy for the CASD-SF was similar to accuracy for the 30-item CASD full form.
