This article presents the psychometric properties of a new measure of social anxiety, the Social Anxiety Questionnaire for adults (SAQ), composed of 30 items that were developed based on participants from 16 Latin American countries, Spain, and Portugal. Two groups of participants were included in the study: a nonclinical group involving 18,133 persons and a clinical group comprising 334 patients with a diagnosis of social anxiety disorder (social phobia). Exploratory and confirmatory factor analyses supported a 5-factor structure of the questionnaire. The factors were labeled as follows: (1) Interactions with strangers, (2) Speaking in public/talking with people in authority, (3) Interactions with the opposite sex, (4) Criticism and embarrassment, and (5) Assertive expression of annoyance, disgust, or displeasure. Psychometric evidence supported the internal consistency, convergent validity, and measurement invariance of the SAQ. To facilitate clinical applications, a receiver operating characteristics (ROC) analysis identified cut scores for men and women for each factor and for the global score.