Individuals with borderline personality disorder (BPD) features may be unaware of or unwilling to report their own personality or maladaptive behaviors, which complicates the assessment of BPD. Informants who know the individuals with BPD features may be uniquely suited to aid in the personality assessment of these individuals. The present study analyzed the comparative ability of individuals (targets) and informants to report BPD features across the continuum of BPD severity. The sample consisted of 1387 targets, ages 55 to 65 (56% women), who were recruited for an epidemiological longitudinal study examining the effects of PDs on health and social functioning. Each target nominated an informant who provided information about the target’s personality. Results indicated relatively low levels of agreement between perspectives and that informants reported BPD symptoms with more precision and at lower levels of BPD severity than targets. The benefits of including an informant perspective when measuring the BPD continuum are discussed; these benefits may include gains in reliability and improvement in the prediction of outcomes.