Screening measures to identify very young children at risk for autism spectrum disorders include the Modified Checklist for Autism in Toddlers (M-CHAT) and the Social Communication Questionnaire (SCQ). To examine the validity of these written questionnaires, parents completed them prior to their child's diagnostic assessment at a tertiary autism clinic. The M-CHAT was given to 84 parents of 2- to 3-year-olds and the SCQ to 94 parents of 4- to 6-year-olds. On both measures sensitivity was higher than specificity with positive predictive values 0.63-0.68. False negatives, or children with autism who were missed by screening, were somewhat higher functioning than true positives. Results were better for parents who spoke English as a second language, contrary to expectations. At this stage of development these tools would be recommended as part of more comprehensive surveillance programmes to identify children in need of further assessment but not to 'screen out' the possibility of autism.