Despite high rates of clinically elevated anxiety difficulties in children and adolescents with autism spectrum disorders (ASDs), very few studies have systematically examined the usefulness of commonly used caregiver report anxiety screening tools with this population. This study investigated the use of the Spence Children's Anxiety Scale-Parent version (SCAS-P) as a screening tool for anxiety disorders when compared to a standardized DSM-IV-TR-based clinical interview, the Kiddie-Schedule for Schizophrenia and Affective Disorders-Present and Lifetime version (K-SADS-PL). Thirty-two caregivers of youth with a clinical diagnosis of ASD (mean age 10.3 years) attending a specialist autism school participated in this study. They first completed the SCAS-P, a measure of adaptive functioning and a checklist of other emotional and behavioral difficulties. They were then interviewed with the K-SADS-PL. Internal consistency for the SCAS Total score was .88, but Cronbach's alphas were <0.70 in three of the six SCAS-P subscales. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the SCAS-P against K-SADS diagnosis were 0.75, 0.71, 0.27, and 0.95, respectively. All values were >0.70, except for the PPV. Evidence of convergent validity between the SCAS-P, K-SADS-PL and DBC anxiety subscale was also found. The high false positive rates notwithstanding, the preliminary data of acceptable to excellent sensitivity, specificity and NPV values tentatively suggest that the SCAS-P may be useful for screening non-help seeking young people with ASD for elevated anxiety symptoms. Further replication in larger studies is needed and ways in which the SCAS-P could be further developed and investigated for use with youth with ASD are discussed.