The aim of the present study was to assess the effect of initial level of psychiatric severity on treatment outcome in psychodynamic therapy and dialectical behavior therapy (DBT) for borderline personality disorder (BPD). It was hypothesized that DBT would lead to better outcome for patients with high psychiatric severity, whereas dynamic treatment would lead to better outcome for patients with lower psychiatric severity. Data from the 5th-year follow-up of the Stockholm City Council’s and the Karolinska Institute’s Psychotherapy Project were used in the present study. A total of 106 female patients diagnosed with BPD with at least 2 past suicide attempts were randomized into object-relational psychotherapy (ORP; based on transference-focused psychotherapy), DBT, and treatment as usual. Patients’ baseline global severity index was used as a moderator. Global Assessment of Functioning (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition [American Psychiatric Association, 1994]) was used to examine outcome. There was a significant 3-way interaction of Time × Treatment × Severity. Post hoc analyses suggested that patients with lower levels of severity had significantly better outcomes in object-relational psychotherapy. For patients with higher severity, the 3 treatments resulted in similar outcomes in terms of level of functioning. Outcome of treatment for BPD might differ significantly for patients depending on their initial levels of overall psychiatric severity. If our findings are replicated for patients with low severity and supported for a high-severity sample, psychiatric severity can be used as a low-cost and effective tool to match patients with BPD to optimal treatments.