This qualitative archival outcome study was designed to assess the effectiveness of intensive outpatient Dialectical Behavior Therapy (DBT) for 36 female clients diagnosed with Borderline Personality Disorder. Clients received 2.75 hours of group DBT per day, three days per week, for at least one year. Decreased frequency of self-injurious behavior (SIB), psychiatric hospital admissions, and prevalence of subjects attempting suicide defined effectiveness in this study. Decreases in the frequency of SIB, psychiatric hospital admissions, and prevalence of subjects attempting suicide were hypothesized when comparing the first and last six months of therapy. The application of intensive outpatient DBT produced statistically significant moderate and large effect-size reductions in the frequency of SIB and psychiatric hospitalizations respectively. The prevalence of subjects attempting suicide was not found statistically significant. This study supports the application of intensive outpatient DBT for treating clients diagnosed with Borderline Personality Disorder as an effective treatment to reduce SIB and psychiatric hospitalization