There has been growing evidence to support the role of impulsive and aggressive behaviors in the risk of suicide. Studies assessing living patients with major depressive disorder have indicated that suicide attempters have higher levels of impulsive and aggressive behaviors (20–24). Similarly, studies looking at the prevalence of these traits in other diagnostic categories have also suggested that attempters are more likely to be impulsive and aggressive (25–29). However, data on impulsive and aggressive behaviors in suicide completers are limited and based primarily on indirect evidence, such as the prevalence of diagnostic categories associated with aggressive and impulsive traits. These studies showed that substance use disorders (1) and borderline personality disorders (30) are associated with an increased risk of suicide when they are comorbid with major depressive disorder. The few studies that carried out direct personality trait assessments remain controversial. Two studies found an association between aggression and suicide (31, 32), but one recent study in adults ages 50 and over showed that the association between aggression and suicide was no longer significant when the authors controlled for psychopathology (33). Therefore, it remains unclear whether the association between impulsive and aggressive behaviors and the risk of suicide is at least partly explained by axis I disorders that are commonly associated with suicide, such as major depressive disorder. This issue has not been properly addressed because almost all previous studies of suicide have exclusively investigated unselected suicide victims in relation to normal comparison subjects and lacked a psychiatric comparison group. Thus, the purpose of our study was to investigate impulsive and aggressive behaviors and associated psychopathology while we directly controlled for major depressive disorder. More specifically, we investigated subjects who committed suicide in the context of a major depressive episode and compared them to a group of age- and gender-matched living subjects with a current major depressive episode of sufficient severity to warrant treatment in a specialized psychiatric outpatient clinic but without a history of medically serious suicide attempts. A key methodological innovation in this study was the use of a proxy informant for both the suicide group, when it was necessary, and also for the living depressed comparison subjects to prevent a reporting artifact because of the method of data collection.