Avoidant personality disorder has been reported to have lifetime prevalence rates of 1.1% and 1.3%, considerably lower than the 13.3% for the related social anxiety disorder reported by Kessler and colleagues in the National Comorbidity Study. The essential feature of avoidant personality disorder was defined in DSM-III-R (American Psychiatric Association 1987) as “a pervasive” pattern of social discomfort, fear of negative evaluation, and timidity, beginning by early childhood and present in a variety of contexts. Although there are few data concerning the implications of having avoidant personality disorder per se, evidence indicates that comorbidity of other disorders with avoidant personality disorder can be a predictor of poorer response to treatment and also higher future morbidity. Alnaes and Torgersen did a prospective analysis of almost 300 outpatients with various diagnoses and found that only the presence of avoidant personality disorder or borderline personality disorder predicted development of new cases of major depression 6 years later. Individuals with major depression and avoidant personality disorder have been shown to have significantly greater social dysfunction than those with major depression only.

Several investigators have suggested that avoidant personality disorder and generalized social phobia are not distinct entities, but represent groups with different levels of severity on a continuum. Empirical studies of the DSM-III and DSM-III-R diagnoses have reported high rates of comorbidity of social anxiety disorder and avoidant personality, ranging from 25% to 89% (median = 57.6%) for the generalized type, with lower rates of 0%-44% (median = 17.5%) reported for the nongeneralized type. Widiger pointed out, in his review of three studies on the validity of the distinction between generalized social phobia and avoidant personality disorder, that “there were many cases of [generalized social phobia] without avoidant personality disorder but few cases of avoidant personality disorder without [generalized social phobia]”. Two of the studies were conducted in an anxiety disorders clinic, possibly biasing the results, and the third used media advertisements soliciting persons with extreme shyness and social anxiety. All three studies reported a lack of findings that would distinguish generalized social phobia and avoidant personality disorder as separate disorders and concluded that the differences were primarily in the severity of symptoms. Widiger noted that information about long-term functioning in each of these categories, as well as large-scale epidemiological studies, can help to determine whether qualitative differences exist. He suggested that if no meaningful distinction can be found, a case can be made for classifying a new generalized social phobia-avoidant personality disorder diagnosis on both Axis I and Axis II, thus defining a new “boundary condition that includes features of both an anxiety and a personality disorder”.

Along with the well-recognized overlap between avoidant personality disorder and generalized social phobia, evidence shows the distinctiveness of avoidant personality disorder. According to Millon, avoidant personality disorder is essentially a problem of relating to persons, in contrast to social phobia, which is largely a problem of performing situations. Others have suggested that the one defining trait in avoidant personality disorder might be interpersonal sensitivity, whereas in social anxiety disorder, it is avoidance of social situations. There are multiple reports of patients meeting the DSM-III-R criteria for avoidant personality disorder but not the criteria for social phobia. Tran and Chambless compared generalized social phobia groups with and without avoidant personality disorder with a group with circumscribed social phobia and found more social impairment and distress in the two generalized groups and more depression in the group with avoidant personality disorder. They concluded that the subtype distinction and the avoidant personality disorder diagnosis were useful. In a sample of 243 outpatients with major depression, 61% of those with comorbid avoidant personality disorder also met criteria for social phobia, but 15% of these subjects met criteria for avoidant personality disorder but not social phobia.

Clinically, although avoidant personality disorder generally responds to typical treatments for social phobia, it may respond differentially and less robustly. Although two treatment studies that used cognitive-behavioral group treatment reported that the presence of avoidant personality disorder in a group of subjects with social phobia had no significant effect on the response to treatment, a third study, which used eclectic behavior therapy, found that the generalized social phobia patients with avoidant personality disorder reported less improvement on overall functioning, but not on social anxiety, than those without the personality disorder at the end of the study. A 12-week retrospective chart study of venlafaxine in a group of patients resistant to selective serotonin reuptake inhibitors (SSRIs) showed good response for those with social phobia but not those with avoidant personality disorder.