The Brief Social Phobia Scale (BSPS) is an observer-rated scale designed to assess the characteristic symptoms of social phobia, using three subscales – fear, avoidance, and physiological arousal – which may be combined into a total score. Each of 18 BSPS items is anchored to a 5-point rating scale. Psychometric evaluation of the BSPS in a sample of 275 social-phobia patients yielded a high level of reliability and validity. Test–retest reliability was excellent, as was internal consistency. The fear and avoidance subscales demonstrated highly significant correlations with remaining item totals; however, the physiological subscale did not. The BSPS also demonstrated significant relationships with other established scales that assess anxiety and disability, and it proved sensitive to treatment effects in a trial of a 5-HT3 antagonist and placebo. Factor analysis yielded six meaningful factors. We conclude that the BSPS provides a reliable, valid, and sensitive measure for the evaluation of social phobia.