--- - |2+ Abstract Objective Diagnoses of personality disorders (PD) must rely on judgments of observers—either clinicians or acquaintances—because personality disorders are primarily defined in terms of maladaptive interpersonal behavior. Little is known, however, about how closely acquaintances' judgments of PD traits relate to self‐reports of theoretically relevant Big Five traits or directly observed behavioral outcomes in interpersonal situations. The present study examines associations between judgments of the 10 PD traits provided by close acquaintances, self‐reports of PD‐relevant Big Five personality traits, and observed interpersonal behaviors across three different three‐person laboratory interactions (i.e., unstructured chat, cooperative task, competitive game). Method The sample consisted of 256 undergraduate students (130 females; Mage = 19.83, SD = 1.25). Four unacquainted observers independently rated participants' behaviors from video recordings. Results In line with previous work, informant reports of PD traits demonstrate strong convergent validity with relevant self‐reported Big Five traits (as identified by Lynam & Widiger, 2001). Directly observed behavior is meaningfully associated with acquaintances' judgments and self‐reports of PD‐relevant traits, and the associations between these judgments and behavior are strongest for traits associated with histrionic and schizoid PD. Vector correlations between behavioral profiles associated with informant and self‐reports show that both assessments have similar behavioral correlates. Associations between PD trait ratings and behavior appeared to differ as a function of gender, with males showing more and stronger correlations. Conclusions Informants' ratings of PD traits are impressively accurate, converging both with self‐reports of relevant traits and directly observed interpersonal behavior. Therefore, a comprehensive understanding of PDs and associated traits can be augmented by information from multiple acquaintances who have the opportunity to observe how an individual interacts with others on a daily basis across diverse contexts. - Journal of Personality, EarlyView.