It has long been assumed that features associated with psychopathy, such as a lack of insight and deceitfulness, may compromise the utility of self-report measures, particularly for understanding the relations between these traits and important outcomes (e.g., offending). Unfortunately, little research has explicitly examined the relations between self- and informant reports of psychopathy and their relations to these outcomes. The current study examined the incremental validity of self- and informant reports of psychopathic traits, assessed with 3 validated psychopathy measures, in the statistical prediction of externalizing behaviors (EBs). To reduce shared method variance, self- and informant reports of EBs (i.e., substance use, antisocial behavior, gambling, and intimate partner violence) were examined separately. Results indicate that both self- and informant reports of psychopathy are related to EBs and provide some degree of incremental validity, although self-reported psychopathy scores proved slightly more useful than other-reported psychopathy scores. These findings suggest that, in nonforensic settings, psychopathy data derived from both self- and other-reported psychopathy measures have utility in understanding the relations between psychopathic traits and EBs.