Despite research documenting a relationship between social anxiety and perfectionism, very little research has examined the relationship between social anxiety and clinical perfectionism, defined as the combination of high personal standards and high maladaptive perfectionistic evaluative concern. In the current studies we examined whether clinical perfectionism predicted social anxiety in a large sample of undergraduates (N = 602), in a clinical sample of participants diagnosed with social anxiety disorder (SAD; N = 180), and by using a variance decomposition model of self-and informant-report of perfectionism (N = 134). Using self-report, we found that an interaction of personal standards and evaluative concern predicted both social interaction anxiety and fear of scrutiny, but not in the theorized direction. Specifically, we found that self-report of low standards and high evaluative concern was associated with the highest levels of social anxiety, suggesting that when individuals with SAD hold low expectations for themselves combined with high concerns about evaluation, social anxiety symptoms may increase. Alternatively, when an informants’ perspective was considered, and more consistent with the original theory, we found that the interaction of informant-only report of personal standards and shared-report (between both primary participant and informant) of concern over mistakes was associated with self-reported social anxiety, such that high concern over mistakes and high personal standards predicted the highest levels of social anxiety. Theoretical, clinical, and measurement implications for clinical perfectionism are discussed.