Borderline personality disorder (BPD) is often characterized by multiple low lethality suicide attempts triggered by seemingly minor incidents, and less commonly by high lethality attempts that are attributed to impulsiveness or comorbid major depression. The relationships among life events, impulsiveness, and type of suicidal behavior has hardly been studied in BPD and mood disorders. This study compared depressed attempters with and without BPD to identify specific suicide precipitants and risk factors in BPD and their relationship to severity of suicidal behavior. Attempters with comorbid BPD and major depressive disorder (MDD) had a higher number of lifetime suicide attempts; made their first attempt at a younger age; reported more interpersonal triggers; and had higher levels of lifetime aggression, hostility, and impulsivity, compared with attempters with major depression only. Environmental triggers of attempts in BPD are more likely to be interpersonal stressors. Lethality of attempts in BPD plus MDD is equal to that in MDD only, indicating that the seriousness of precipitants is unrelated to the lethality of the suicidal behavior. The differences between groups suggest that risk assessment and treatment should target both depression and personality disorder in those with combined illness.