Behavior and emotional problems are often present in very young children with autism spectrum disorders (ASDs) but their nosology has been the object of scant empirical attention. The objective of this study was to assess the construct validity of select Diagnostic and Statistical Manual of Mental Disorders (DSM)–defined syndromes (ADHD, ODD, Mood disorder) in preschoolers with ASD (N = 229). Parents and teachers completed the Early Childhood Inventory–4, a behavior rating scale based on the DSM-IV, and ratings were submitted to confirmatory factor analysis. Results generally supported the DSM nosology in this population. There was some evidence that parent ratings were associated with better fit indices (e.g. RSMEA = .062) than teachers (e.g. RMSEA = .083). For both raters, fit indices appeared to improve when the ADHD factor was broken into its constituent parts. However, hyperactivity symptoms accounted for little unique additional variance in the model. Findings lend support to the DSM as a conceptual model for behavioral syndromes in preschoolers with ASDs and also reinforce the importance of source-specificity when considering psychiatric disorders in children with ASDs.