Premature termination from group psychotherapy continues to be a serious problem in the treatment of patients with borderline personality disorder (BPD). Qualitative research is regarded as an important means to shed light upon the complex dynamics leading to dropout. We conducted an interview study with patients having a diagnosis of BPD (n = 8) who dropped out from long-term group psychotherapy as a continuation therapy following intensive day treatment. The group therapists for these patients were interviewed as well (n = 12). The findings suggest the operation of many processes that contribute to dropout. Most significant appeared to be experiences of separation and loss of the day hospital that were not worked through and a failure of the group to regulate and contain the patients' affects. To integrate patients at risk of premature termination it seems necessary to pay attention to the strong negative emotions that they experience in the group. A higher treatment intensity than weekly group sessions may help to promote more beneficial group processes.