Theories of anxiety disorders and phobias have ascribed a critical role to avoidance behavior in explaining the persistence of fear and anxiety, but knowledge about the role of avoidance behavior in the maintenance of anxiety in social anxiety disorder relative to specific phobia is lacking. This study examined the extent to which avoidance behavior moderates the relationship between general anxiety at baseline and 18 months later in women with a diagnosed social anxiety disorder (n = 91) and women with a diagnosed specific phobia (n = 130) at baseline. Circumscribed avoidance of social and specific situations were clinician-rated using the Anxiety Disorders Interview Schedule-Lifetime (ADIS-IV-L), and general anxiety was measured using the Beck Anxiety Inventory (BAI). Moderated regression analyses revealed that (a) general anxiety at baseline predicted general anxiety at follow-up in both women with a specific phobia and women with a social anxiety disorder and (b) avoidance behavior moderated this relationship in women with a specific phobia but not in women with a social anxiety disorder. Specifically, high avoidance behavior was found to amplify the effect between general anxiety at baseline and follow-up in specific phobia. Reasons for the absence of a similar moderating effect of avoidance behavior within social anxiety disorder are discussed.