The present study aims to develop an assessment instrument for children with Autism Spectrum Disorders (ASD) in Turkey based on the Autism Behavior Checklist (ABC). Validity and reliability studies of Adapted ABC (AABC) were conducted on 969 children with ASD and 164 children with intellectual disability from 21 cities in Turkey. Exploratory and confirmatory factor analyses revealed a two-factor structure. The correlation of the AABC with the Gilliam Autism Rating Scale-2-Turkish Version supported criterion-referenced validity. Reliability analyses demonstrated that test–retest, internal consistency, and item discrimination reliability levels met the required conditions. Finally, the score equivalents of the percentiles required to use the instrument in accordance with the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM V), were determined.