A top priority in the field of autism spectrum disorders (ASD) is the development of precise early diagnostic tools that can be completed with minimal time and training. We report on the convergent and divergent validity of the Baby and Infant Screen for Children with aUtIsm Traits (BISCUIT), specifically the BISCUIT-Part 1. Previous research with this scale has determined its reliability and sensitivity/specificity. In this study, a sample of 1,007 toddlers 17–37 months of age were assessed individually. The BISCUIT-Part 1 demonstrated good convergent validity with the Modified CHecklist for Autism in Toddlers (M-CHAT) and the Personal Social domain from the Battelle Developmental Inventory, Second Edition (BDI-2). Additionally, divergent validity was demonstrated by its small correlation with the Adaptive and Motor domains from the BDI-2.