The assessment instruments for diagnosing children with autism spectrum disorder have been developed mostly in affluent, English-speaking countries. Among the most popular has been the Autism Diagnostic Interview--Revised. This article reports its use in Iran with the dual aims of confirming the factor structure of the revised Autism Diagnostic Interview when used to assess Iranian children for autism spectrum disorder and to identify the algorithms that best distinguish children with autism spectrum disorder from those who are developing typically and from those with intellectual disability. Study 1 contrasted the Autism Diagnostic Interview--Revised ratings given to 420 children with autism spectrum disorder from those of 110 typically developing children. In Study 2, the Autism Diagnostic Interview--Revised ratings of 720 children with autism spectrum disorder were compared with those of 172 children with intellectual disability, and from those with intellectual disability. Exploratory factor analyses identified one main factor that merged the social interaction and communication items of Autism Diagnostic Interview--Revised, but replicated the repetitive behaviour and verbal factors. Receiver operating characteristic analyses identified suitable cut-off points on the revised factor scores. Also, the age at which symptoms became apparent increased the sensitivity of the algorithm in distinguishing children with autism spectrum disorder from those with intellectual disability. These findings are in line with the "Diagnostic and Statistical Manual of Mental Disorders" (5th ed.), recommendations and suggest a commonality in autism spectrum disorder presentations across different nations. The methodology used in this research could guide similar adaptations of assessment instruments for use in other cultures.