The Anxiety Sensitivity Index-3 (ASI-3) is an 18-item measure, recently developed to assess AS, based, consisting of Physical Concerns (eg, the belief that palpitations lead to a cardiac arrest), Social Concerns (eg, the belief that publicly observable anxiety reactions will elicit social refusal), and Cognitive Concerns (eg, the belief that cognitive difficulties lead to insanity). In the Italian context there is a lack of a validated measure of AS, to date.The current study assessed factor structure, reliability, and validity of the Italian ASI-3 in large community and clinical samples. The Italian ASI-3, the Beck Depression Inventory-II, and the State and Trait Anxiety Inventory-trait subscale were administered to 547 community individuals and 146 patients with a primary panic disorder (PD) (n= 30), generalized anxiety disorder (GAD) (n= 33), social phobia (SPh) (n= 25), or psychosis (PSY) (n= 28). Exploratory and confirmatory factor analyses supported the three dimensions of AS in the community sample. All the ASI-3 dimensions showed good to excellent internal consistency, and moderate correlations with depression and trait anxiety measures. Physical Concerns discriminated PD patients from community individuals and the other clinical groups. Social Concerns discriminated SPh patients from community individuals and the other clinical groups. Patients with anxiety disorders had comparable scores on Cognitive Concerns and higher than community individuals. Patients with GAD endorsed higher scores than patients with PSY, specifically. Theoretical explanations, implication for research, and limitations are discussed.