Course and outcome of Borderline Personality Disorder (BPD) are favorable for the vast majority of patients; however, up to 10% die by suicide. This discrepancy begs the question of whether there is a high lethality subtype in BPD, defined by recurrent suicidal behavior and increasing attempt lethality over time. In a prospective, longitudinal study, we sought predictors of high lethality among repeat attempters, and defined clinical subtypes by applying trajectory analysis to consecutive lethality scores. Criteria-defined subjects with BPD were assessed using standardized instruments and followed longitudinally. Suicidal behavior was assessed on the Columbia Suicide History, Lethality Rating Scale, and Suicide Intent Scale. Variables discriminating single and repeat attempters were entered into logistic regression models to define predictors of high and low lethality attempts. Trajectory analysis using three attempt and five attempt models identified discrete patterns of Lethality Rating Scale scores. A high lethality trajectory was associated with inpatient recruitment, and poor psychosocial function, a low lethality trajectory with greater Negativism, Substance Use Disorders, Histrionic and/or Narcissistic PD co-morbidity. Illness severity, older age, and poor psychosocial function are characteristics of a poor prognosis subtype related to suicidal behavior.