Introduction: The recording of negative effects (nE) of psychotherapy (PT) is important in order to identify weak points of PT and to improve the quality of treatment. The aim of the study is to find out which nE patients describe after day-clinic treatment for borderline personality disorders (BPD) with a dialectical behavioral therapy (DBT), which influencing factors are present, and how the content of the complaints is to be understood. Material and Methods: 22.6 months after the end of therapy, BPS patients were asked catamnestically which nE they remembered in relation to a 12-week day-clinic treatment. Measuring instruments were BDI, BSL-95, and INEP. Results: 35 women and 6 men answered (50% of 82). A mean of 11.2 nE was named, which was subjectively attributed to the DBT treatment. 97.6% report worsening of their condition, 87.8% recall problems in the therapeutic relationship, 43.9% report deterioration in their relationship, 70.7% report financial problems as a result of day-clinic treatment, and 29.3% about experience of stigmatization. The number of nE correlated with older age at the start of therapy (p < 0.01) and higher symptom burden based on the BSL-95 (p < 0.01) and BDI (p < 0.01) at the time of the survey. Discussion: It could be shown that when using the INEP, patients complain of considerable rates of negative experiences in the context of day-clinic treatment. The long recall period of 3 to 51 months and the correlation with the current symptoms call the validity of the answer into question. Results of self-rating instruments for recording side effects require very careful interpretation. (c) 2020 The Author(s) Published by S. Karger AG, Basel