Social anxiety disorder has only recently garnered recognition as a unique anxiety disorder. Although social anxiety disorder is distinguishable from other psychiatric disorders, there are several areas in which this distinction is not straightforward. Furthermore, social anxiety disorder is associated with considerable comorbidity with other disorders, which may render differential diagnosis a challenging endeavor. This article will review those disorders that must be differentiated from social anxiety disorder, including major depression, panic disorder with agoraphobia, generalized anxiety disorder, obsessive-compulsive disorder, and body dysmorphic disorder. In addition, the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) provides specific examples of disorders, e.g., verbal dysfluency (stuttering) and Parkinson's disease, in the context of which social anxiety disorder is not to be diagnosed. Social anxiety disorder is also frequently comorbid with the Axis II avoidant personality disorder. Interestingly, this may present a prime example of "comorbidity by committee," because it is growing increasingly clear that much avoidant personality disorder as defined by DSM-IV merely denotes a subgroup of patients with generalized social anxiety disorder. Because social anxiety disorder has a chronic course and is associated with significant morbidity, it is critical that patients receive an accurate diagnosis and appropriate treatment.