BACKGROUND: Identifying anxiety disorders in preschool-age children represents an important clinical challenge. Observation is essential to clinical assessment and can help differentiate normative variation from clinically significant anxiety. Yet, most anxiety assessment methods for young children rely on parent-reports. The goal of this article is to present and preliminarily test the reliability and validity of a novel observational paradigm for assessing a range of fearful and anxious behaviors in young children, the Anxiety Dimensional Observation Schedule (Anx-DOS). METHODS: A diverse sample of 403 children, aged 3 to 6 years, and their mothers was studied. Reliability and validity in relation to parent reports (Preschool Age Psychiatric Assessment) and known risk factors, including indicators of behavioral inhibition (latency to touch novel objects) and attention bias to threat (in the dot-probe task) were investigated. RESULTS: The Anx-DOS demonstrated good inter-rater reliability and internal consistency. Evidence for convergent validity was demonstrated relative to mother-reported separation anxiety, social anxiety, phobic avoidance, trauma symptoms, and past service use. Finally, fearfulness was associated with observed latency and attention bias toward threat. CONCLUSIONS: Findings support the Anx-DOS as a method for capturing early manifestations of fearfulness and anxiety in young children. Multimethod assessments incorporating standardized methods for assessing discrete, observable manifestations of anxiety may be beneficial for early identification and clinical intervention efforts.