Cognitive behavioral models of social anxiety disorder (SAD) suggest that fear of negative evaluation is a core fear or vulnerability for SAD. However, why negative evaluation is feared is not fully understood. It is possible that core beliefs contribute to the relationship between fear of negative evaluation and SAD. One of these beliefs may be a core extrusion schema: a constellation of beliefs that one’s true self will be rejected by others and therefore one should hide one’s true self. In the current study (N = 699), we extended research on the Core Extrusion Schema and created a shortened and revised version of the measure called the Core Extrusion Schema–Revised. The Core Extrusion Schema–Revised demonstrated good factor fit for its two subscales (Hidden Self and Rejection of the True Self) and was invariant across gender and ethnicity. The Hidden Self subscale demonstrated excellent incremental validity within the full sample as well as in participants diagnosed with generalized SAD. Specifically, the Hidden Self subscale may help explain severity of social interaction anxiety. This measure could be used with individuals diagnosed with generalized SAD to design exposures targeting these core beliefs.