Failure to begin speaking, or acquiring words and word combinations, is the most common presenting problem in young children. For children with very limited communication skills, it can be difficult to differentiate between children suffering from autism spectrum disorders (ASD) and those with a more circumscribed delay in language development (DLD). This article reviews evidence derived from studies of toddlers who present with poor communication and social skills and summarizes characteristics of early development in these children to assist clinicians in differentiating between ASD and DLD in toddlers.