The relationship between co-occurring personality disorders and anxiety disorders (panic disorder with or without agoraphobia, social phobia, and generalized anxiety disorder) was examined, taking into account the effect of major depression. This article describes findings for 622 participants in the Harvard/Brown Anxiety Research Project, a longitudinal follow-up study of DSM-III-R-defined anxiety disorders. A total of 24% of participants had at least one personality disorder, with avoidant, obsessive compulsive, dependent, and borderline most common. Generalized anxiety disorder, social phobia, and major depression were positively associated with the occurrence of one or more personality disorders, whereas panic disorder with agoraphobia was not associated. Major depression was associated in particular with dependent, borderline, histrionic, and obsessive compulsive personality disorders and social phobia was associated with avoidant personality disorder. Whereas some of our findings confirm results from earlier studies, others are somewhat inconsistent with previous results and indicate the need for further investigation.