Co-occurring anxiety is common in children with autism spectrum disorder (ASD). However, inconsistencies across parent and child reports of anxiety may complicate the assessment of anxiety in this population. The present study examined parent and child anxiety ratings in children with ASD with and without anxiety disorders and tested the association between parent-child anxiety rating discrepancy and ASD symptom severity. Participants included children aged 8-16 years in three diagnostic groups: ASD with co-occurring anxiety disorders (ASD + Anxiety; n = 34), ASD without co-occurring anxiety disorders (ASD; n = 18), and typically developing healthy controls (TD; n = 50). Parents and children completed ratings of child anxiety using the Multidimensional Anxiety Rating Scale. Patterns of parent and child anxiety ratings differed among the three groups, with parent ratings exceeding child ratings only in the ASD + Anxiety group. Parents reported higher levels of child anxiety in the ASD + Anxiety versus ASD group, whereas children reported comparable levels of anxiety in the two groups. Among children with ASD, ASD symptom severity was positively associated with the degree to which parent ratings exceeded child ratings. Results suggest that children with ASD and co-occurring anxiety disorders endorse some anxiety symptoms but may underreport overall levels of anxiety. In addition, ASD symptom severity might increase discrepancies in parent-child anxiety ratings. These findings suggest a unique and valuable role of child anxiety ratings and suggest that both parent and child anxiety ratings should be considered in light of children's ASD symptom severity and used to guide further assessment. Autism Res 2020, 13: 93-103. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Children with autism spectrum disorder (ASD) commonly experience anxiety; yet, their perceptions of their anxiety might differ from their parents' perceptions. This study found that, while children with ASD and anxiety disorders acknowledge some anxiety, their parents report them as having higher levels of anxiety. Also, child and parent perceptions of anxiety may differ more for children with more severe ASD symptoms. How these findings may guide research and clinical practice is discussed.