The study investigated if the degree of personality pathology among people with clinical levels of social anxiety disorder was similar to those with personality disorders more generally, if the degree of avoidant personality pathology was correlated positively with Neuroticism and negatively with Extraversion and facets of Agreeableness (particularly Trust), and finally if scores on the relevant personality dimensions improve from pre- to post-treatment. Changes in Neuroticism, Extraversion, and Agreeableness were examined following group treatment for social anxiety disorder. The current study employed a within-subjects repeated-measures design (N = 25) to investigate whether these traits can be changed by group treatment for social anxiety disorder. A measure of personality disorder pathology was found to correlate positively with Neuroticism and negatively with Agreeableness in the absence of significant relationships with other Five-Factor Model traits. Treatment was associated with significant reductions in Neuroticism and there was significant improvement of the Trust facet of Agreeableness. These results are discussed in terms of the way that group treatment for Social Anxiety Disorder may be enhanced.