Children with autism spectrum disorder (ASD) exhibit high rates of challenging behaviors that impair functioning and represent the primary presenting problem in mental health (MH) services. Obtaining symptom reports from multiple informants is critical for treatment planning. This study evaluated caregiver-teacher concordance of ratings of the intensity of challenging behaviors in children with ASD receiving MH services, and identified child clinical factors associated with concordance. This sample included 141 children (M = 9.07 years), their caregivers, and teachers. Caregiver-teacher concordance of challenging behaviors was low and impacted by the degree and type of child psychiatric comorbidity. Findings support need for increased attention to the range of psychiatric problems children with ASD present to tailor treatment recommendations and service delivery.