Co-rumination is an interpersonal emotion regulation strategy characterized by extensive, cyclical conversations regarding the causes and consequences of problems and associated negative emotions. Theory posits that over time, interpersonal benefits of co-rumination such as emotional intimacy reinforce the behavior, outweighing the resulting negative impacts on mental health. However, our understanding of how co-rumination is perpetuated within conversations is limited. This study (conducted in 2019-2020) aims to assess perceptions of partner co-rumination and responsiveness as factors that perpetuate co-rumination to better understand the intra- and interpersonal processes that influence how co-rumination unfolds within conversations. To do this, we utilized an observational paradigm with primarily White, female, young adult friendship dyads wherein one individual (the discloser) disclosed and discussed an extradyadic problem with a close friend (the responder). Using an empathic accuracy paradigm, participants reported their own and their partner's co-rumination and responsiveness for every 30-s epoch. Results revealed biased estimations of partner co-rumination that may facilitate reciprocity of co-ruminative conversation within the dyad. Additionally, while greater perceptions of partner co-rumination were perceived as responsive by disclosers and elicited responsive behavior from responders, perceived partner responsiveness did not perpetuate co-rumination within the conversation. Together, these findings enhance our understanding of the intra- and interpersonal processes that influence how co-rumination unfolds within conversations between close friends, but they also draw attention to unanswered questions in the field regarding partner contributions to co-rumination, the nature of problems discussed, and generalizability of these findings as well as those of other extant co-rumination research. (PsycInfo Database Record (c) 2024 APA, all rights reserved).