Irritability is an impairing problem in children with ASD that may be associated with other behavioral and emotional concerns. The Affective Reactivity Index (ARI) is a parent-rated measure of irritability widely used in children with mood disorders, however, its utility in children with ASD remains unclear. In this study, we examined ARI parent ratings in children with ASD and contributions of parent-rated anxiety and noncompliance to irritability measured by the ARI. Participants included 81 children with ASD, aged 8-16 years. Results suggest that both anxiety and noncompliance contribute to irritability, but that anxiety only contributes to irritability in the absence of noncompliance. Further, the ARI is likely to be a useful measure of irritability in children with ASD.