Early detection and treatment have been shown to be effective in reducing disability severity caused by Autistic Spectrum Disorders (ASDs). As Spanish pediatricians have no detection tool, the Modified Checklist for Autism in Toddlers (M-CHAT) was first translated into and culturally adapted to Spanish. Validity and reliability studies were carried out in two different geographical areas of Spain, where M-CHAT was administered to two different samples, namely: 2,480 high- and low-risk children; and 2,055 low-risk children. The results obtained were similar to those yielded by the original M-CHAT studies. Differences were found in positive predictive value, due to the low ASD frequency observed in this study. M-CHAT is still being studied in a large population-based screening program in Spain.

A large number of studies have reported on the validity of autism spectrum disorder (ASD) screening procedures. An overall understanding of these studies' findings cannot be based solely on the level of internal validity of each, since screening instruments might perform differently according to certain factors in different settings. Europe has led the field with the development of the first screening tool and first prospective screening study of autism. This paper seeks to provide an overview of ASD screening studies and ongoing programmes across Europe, and identify variables that have influenced the outcomes of such studies. Results show that, to date, over 70,000 children have been screened in Europe using 18 different screening procedures. Differences among findings across studies have enabled us to identify ten factors that may influence screening results. Although it is impossible to draw firm conclusions as to which screening procedure is most effective, this analysis might facilitate the choice of a screening method that best fits a specific scenario, and this, in turn, may eventually improve early ASD detection procedures.

TS translated the surveys into their native languages and disseminated them in their respective countries. All authors have read and approved the final manuscript.