Prior work points to a subtype of Social Anxiety (SA) characterized by disinhibition or high externalizing behaviors (e.g., substance use and Attention Deficit Hyperactivity Disorder (ADHD) symptoms). This study extended prior work by replicating subtypes of SA and impulsivity and examining differences among these subtypes in their expression of externalizing behavior. Three hundred seventy-five undergraduates completed an online study including measures of SA, substance use, ADHD symptoms and impulsivity. Latent class analyses revealed three classes of individuals who were: (a) low SA and low impulsivity, (b) high SA and low impulsivity, and (c) high SA and high impulsivity. Individuals high in both SA and impulsivity exhibited greater likelihoods of exhibiting externalizing behavior concerns, relative to the two other classes, with the largest differences on ADHD symptoms. These findings indicate that identifying differences among SA subtypes in externalizing behavior concerns depends on the externalizing domain.