This article describes the development of a screening instrument for young children. Screening items were tested first in a non-selected population of children aged 8-20 months (n = 478). Then, parents of children with clinically diagnosed ASD (n = 153, average age 87 months) or ADHD (n = 76, average age 112 months) were asked to score the items retrospectively for when their child was 14 months old. A 14-item screening instrument, Early Screening of Autistic Traits (ESAT) which had maximal sensitivity and specificity for ASD was developed. The sensitivity of the ESAT was checked in an independent sample of 34 children aged 16-48 months clinically diagnosed with ASD. A 4-item version appears to be a promising prescreening instrument.