Abstract
The purpose of this study is to investigate the role of rumination about an interpersonal offense (RIO) in mediating borderline personality traits and depression. The sample for this study was determined by random sampling, and the participants were 419 people, 218 women (52%) and 201 men (48%), aged 18-35, residing in Istanbul in 2022 and who willingly participated in the research. The participants were administered the Sociodemographic data form, the Borderline Personality Questionnaire (BPQ), the Zung Depression Scale (ZDS), and the Rumination about an Interpersonal Offense Scale (RIO), and the data obtained in the study were analyzed using SPSS 25.0. Pearson correlation analysis, the independent group t-tests, ANOVA, and PROCESS 3.5 were used. The confidence interval referenced in the whole study was 95%, and the p value was 0.05. The study's findings suggest that RIO mediates the relationship between depressive symptoms and borderline personality characteristics. RIO, borderline personality traits (r=.525, p0.01), and depression (r=.524, p0.01) were revealed to be positively and significantly correlated. It has been claimed that people with borderline personality characteristics may use rumination as a maladaptive coping method in their interpersonal relationships. It has been determined that individuals with borderline personality features may have other-oriented ruminative tendencies, and RIO can be described as a cognitive vulnerability in borderline personality disorder (BPD). It is advised to reduce RIO and utilize cognitive strategies to replace borderline patients' dysfunctional beliefs about themselves, others, and the world with functional beliefs for the treatment of BPD and its accompanying depressive symptoms.

Key words: Borderline Personality Disorder, Rumination, Interpersonal Offense, Depression