Exact data on the repetition of self-harm over 16-20 week and 12 months observation periods for adolescents in outpatient psychiatric treatment are not available. Building on previous clinical studies and RCT studies in adults receiving DBT, we anticipate that the 16 week repetition rate will be 50% for adolescents who receive EUC and 25% for adolescents who receive DBT. With an alpha error level of 5% 60 patients in each group is needed to provide 80% power with a two tailed test. We anticipate a drop out rate from research assessments of no more than 25%. To compensate for this attrition, it is calculated that 15 patients in each treatment group should be added, leading to a total number of 150 patients to be included in the trial. A more precise power analysis and determination of how many patients to include in the study will be based on data from the first 40 patients who have been included.