OBJECTIVE: This study identified potential risk factors for suicidal behavior in patients with borderline personality disorder defined by the Diagnostic Interview for Borderline Patients and by DSM-III-R criteria for patients who did and did not attempt suicide. METHOD: Histories of suicide attempts and attempt characteristics were obtained by Schedule for Affective Disorders and Schizophrenia interviews from 84 patients with borderline personality disorder and were related to severity of borderline pathology, diagnostic comorbidity, and state and trait symptoms. RESULTS: There were 61 patients with a lifetime history of suicide attempts (72.6%), with an average of 3.39 (SD = 2.87) attempts per patient. Attempters were significantly older than nonattempters, with more impulse actions, antisocial personality disorder comorbidity, and state depression. State depression was significantly less severe in patients who had attempted suicide in the present episode (or past year) than in patients who had attempted suicide only in the past. A comorbid diagnosis of major depression, alcoholism, or drug use disorder did not distinguish attempters from nonattempters. Suicide attempt in the present episode was best predicted by the number of prior lifetime attempts. A highly serious intent to commit suicide was predicted by the number of lifetime attempts and subjective depression, while a low intent was predicted by a mixed subtype of borderline personality disorder plus schizotypal personality disorder and paranoid ideation. A high degree of medical lethality was predicted by number of lifetime attempts, older age, and hysteroid dysphoria, while low lethality attempts were associated with high degrees of anger. CONCLUSIONS: Risk factors for suicidal behavior in patients with borderline personality disorder include older age, prior suicide attempts, antisocial personality, impulsive actions, and depressive moods but not comorbid affective disorder, alcoholism, or drug use disorders.