Background: The Autism Detection in Early Childhood (ADEC) is a clinician-administered, Level 2 screening tool. A retrospective file audit was used to investigate its clinical effectiveness. Method: Toddlers referred to an Australian child development service between 2008 and 2010 (N = 53, M age = 32.2 months) were screened with the ADEC. Their medical records were reviewed in 2013 when their mean age was 74.5 months, and the original ADEC screening results were compared with later diagnostic outcomes. Results: The ADEC had good sensitivity (87.5%) and moderate specificity (62%). Three behaviours predicted autism spectrum disorders (ASDs): response to name, gaze switching, and gaze monitoring (p = 0.001). Conclusions: The ADEC shows promise as a screening tool that can discriminate between young children with ASDs and those who have specific communication disorders or developmental delays that persist into middle childhood but who do not meet the criteria for ASDs.