Suitable screening instruments for the early diagnosis of autism are not readily available for use with preschoolers in non-Western countries. This study evaluated two tools: M-CHAT which is widely used internationally and one developed in Iran called Hiva. A population sample was recruited of nearly 3000 preschoolers in one Iranian city. Parents self-completed the two tools and children who screened positive were invited for a follow-up interview followed by a diagnostic assessment. The Hiva scale proved to be more efficacious in identifying children with ASD and the resulting prevalence rate was higher than that previously reported for Iranian 5 year olds. The study confirms the need to attune screening tools to the cultural contexts in which they are used.