Individuals with an autism spectrum disorder (ASD) often present with co-occurring emotional and behavioral disorders (EBD). The Child Behavior Checklist 6-18 (CBCL; Achenbach & Rescorla, 2001) is an EBD measure that contains several norm-referenced scales derived through factor analysis of data from the general pediatric population. The psychometric properties of this widely used and well-researched measure have not been evaluated in samples of youth with ASD. This study evaluated the CBCL's internal structure, scale reliability, criterion-related validity, and diagnostic accuracy using archival data from a well-characterized sample of youth with ASD (N = 122). Confirmatory factor analyses supported the unidimensionality of the CBCL's syndrome scales and its internalizing-externalizing factor structure. Significance tests indicated that many scales discriminated between two subgroups: a group of individuals with ASD + EBD and a group with ASD alone. Diagnostic accuracy analyses indicated that the CBCL had good sensitivity but low specificity for detecting co-occurring disorders. Results supported the use of the CBCL in conjunction with other clinical data when assessing for EBD in youth with ASD. (Contains 4 tables and 1 figure.)