Background: The Social Interaction Anxiety Scale and Social Phobia Scale6 are companion measures for assessing symptoms of social anxiety and social phobia. The scales have good reliability and validity across several samples,3, 6 however, exploratory and confirmatory factor analyses have yielded solutions comprising substantially different item content and factor structures. These discrepancies are likely the result of analyzing items from each scale separately or simultaneously. The current investigation sets out to assess items from those scales, both simultaneously and separately, using exploratory and confirmatory factor analyses in an effort to resolve the factor structure. Methods: Participants consisted of a clinical sample (n5353; 54% women) and an undergraduate sample (n5317; 75% women) who completed the Social Interaction Anxiety Scale and Social Phobia Scale, along with additional fear-related measures to assess convergent and discriminant validity. Results: A three-factor solution with a reduced set of items was found to be most stable, irrespective of whether the items from each scale are assessed together or separately. Items from the Social Interaction Anxiety Scale represented one factor, whereas items from the Social Phobia Scale represented two other factors. Conclusion: Initial support for scale and factor validity, along with implications and recommendations for future research, is provided. Depression and Anxiety, 2009. © 2009 Wiley-Liss, Inc.