Numerous authors have theorized that defense mechanisms play a role in personality disorders. We reviewed theoretical writings and empirical studies about defenses in schizotypal, borderline, antisocial, and narcissistic personality disorders, developing hypotheses about these differential relationships. We then examined these hypotheses using dynamic interview data rated for defenses in a study of participants (n = 107) diagnosed with these four personality disorder types. Overall, the prevalence of immature defenses was substantial, and all four disorders fit within the broad borderline personality organization construct. Defenses predicted the most variance in borderline and the least variance in schizotypal personality disorder, suggesting that dynamic factors played the largest role in borderline and the least in schizotypal personality. Central to borderline personality were strong associations with major image-distorting defenses, primarily splitting of self and other's images, and the hysterical level defenses, dissociation and repression. Narcissistic and antisocial personality disorders shared minor image-distorting defenses, such as omnipotence or devaluation, while narcissistic also used splitting of self-images and antisocial used disavowal defenses like denial. Overall, differential relationships between specific defenses and personality disorder types were largely consistent with the literature, and consistent with the importance that the treatment literature ascribes to working with defenses.