Although borderline personality disorder (BPD) is frequently characterized by nonsuicidal self-injurious behavior (NSSI), suicide attempts (SA), suicidal ideation (SI), and/or suicide threats (ST), it is unclear whether these behaviors are precursors of BPD in adolescence. This study examined self-harm/suicide-related behaviors in the development of BPD from adolescence to adulthood in psychiatrically hospitalized adolescents. Participants were 116 adolescents consecutively admitted for a psychiatric hospitalization for self-harm/suicide-related behaviors. Adolescents completed self-report questionnaires assessing self-harm/suicide-related behaviors, maladaptive familial behavior, and peer victimization upon admission. Admission diagnoses and history of sexual/physical abuse were abstracted from medical/psychiatric records. Five years after index hospitalization, medical/psychiatric records were systematically reviewed and information on diagnoses was collected. Using multivariable logistic regression analyses, ST predicted BPD above and beyond NSSI, SA, and SI 5 years later (odds ratio = 1.31, 95% confidence interval [1.06, 1.62], p > .01). Traditional risk factors of BPD were not predictive of BPD at 5-year follow-up. Suicidal threats are an important risk factor in adolescents who engage in self-harm/suicide-related behaviors that may differentiate those adolescents who go on to develop BPD as adults. Implications for research and treatment are discussed.