Negative evaluation fears figure prominently in the cognitive psychology of patients with social phobia. In this study, we examine the heritability of negative evaluation fears by using a twin sample. The authors also examine the relationships between negative evaluation fears and personality dimensions relevant to social phobia. Scores on the brief version of the Fear of Negative Evaluation Scale (BFNE) were examined in a sample of 437 (245 monozygotic and 192 dizygotic) twin pairs. Biometrical model fitting was conducted by using standard statistical methods. Genetic and environmental correlations with personality dimensions (from the Dimensional Assessment of Personality Pathology-Basic Questionnaire) were also calculated. Broad heritability estimate of the BFNE was 48%. Additive genetic effects and unique environmental effects emerged as the primary influences on negative evaluation fears. Genetic correlations between BFNE scores and the submissiveness, anxiousness, and social avoidance facets of the Dimensional Assessment of Personality Pathology-Basic Questionnaire were high (r(g) =.78 to.80). A cognitive dimension central to the phenomenology (and, perhaps, cause) of social phobia, the fear of being negatively evaluated, is moderately heritable. Moreover, the same genes that influence negative evaluation fears appear to influence a cluster of anxiety-related personality characteristics. Implications and limitations of these findings are discussed.