Anxiety is a prevalent co-occurring disorder in autistic youth, yet its accurate assessment remains challenging due to symptom overlap with autism. The Anxiety Scale for Children with Autism Spectrum Disorder—Parent Version (ASC-ASD-P) was designed to address this issue, but its utility in German clinical settings has not been established. This study validated the German translation of the ASC-ASD-P in a clinical sample of 317 participants presenting at a clinic for autism assessment, including 120 autistic youth. Internal consistency was excellent (Cronbach's α = 0.92), and convergent validity was demonstrated through significant correlations with established psychopathology measures such as the Child Behavior Checklist (CBCL) and Strengths and Difficulties Questionnaire (SDQ). Factor analyses preferred a 4-factor structure in the autism group, but indicated difficulties replicating the Separation Anxiety Subscale. Autistic youth showed higher total anxiety and uncertainty scores compared to non-autistic youth, underlining the scale's sensitivity to autism-specific anxiety patterns. By including youth with intellectual disabilities, often underrepresented in research, this study provides a more comprehensive evaluation of the ASC-ASD-P's applicability across the autism spectrum. These findings support the ASC-ASD-P as a reliable tool for assessing anxiety in German-speaking autistic youth while highlighting areas where refinement could strengthen its utility.