The purpose of this study was to examine the effectiveness, and predictors of response and drop-out during a four-week course of intensive dialectical behavior therapy (I-DBT) in 447 outpatients suffering from borderline personality disorder (BPD), over a 10-year period. Assessments included a diagnostic interview, the International Personality Disorder Examination Screening Questionnaire, the Beck Depression Inventory, and the Beck Hopelessness Scale. Among these participants, 103 started a second course of treatment. In agreement with previous reports, I-DBT was effective in reducing levels of depression and hopelessness with a trend of increasing effectiveness over the study period. High schizoid scores and low narcissistic score predicted poor response. Treatment completion rate was high, and low education predicted dropout. A discussion on the usefulness of a second course of treatment should be held with patients and staff as it was not effective in reducing depression and hopelessness.