Research on siblings of youth with autism spectrum disorder (ASD) suggests that some phenotypic presentation, known as the broader autism phenotype (BAP), is common among siblings without an ASD diagnosis (e.g., Ruzich et al. in Autism Res 9(6):658–665, 2016). Whereas the symptoms that underlie both ASD and the BAP share commonality, the structure of these symptoms in youth with ASD and their siblings may differ. The current study assessed whether differences arise in the factor structure of the Children’s Social Behavior Questionnaire (CSBQ) between youth with ASD and their siblings in a sample of 221 sibling dyads. Results suggest similar factor structures for ASD and BAP; however, number of symptoms endorsed, as opposed to the degree of severity, may better differentiate BAP.