Over the past decade, researchers have learned a great deal about the outcomes of corumination, or dyadic tendencies in which two members excessively discuss and revisit problems while focusing on negative feelings (Rose, 2002). Research indicates that corumination is linked to closer friendship quality in youths, but also greater emotional disturbance (e.g., depression and anxiety; Rose, 2002;Rose, Carlson & Waller, 2007). Surprisingly, little is known about the predictors of co-rumination. The current study addressed whether attachment, rumination, and trait depression are predictive of corumination. In addition, this research evaluated co-rumination in relation to interdependence theory by proposing that it is subjected to the impacts from both the individuals' and their friend's attachment representations, rumination, and trait depression. It was hypothesized that more anxiously attached, depressive, and ruminative individuals would engage in more co-rumination with a close friend. Furthermore, it was hypothesized that having a friend who is more anxious, more depressive, or more ruminative may drive an individual to engage in more co-rumination. Results revealed that an individual's attachment avoidance was significantly related to their own (actor effect) and their friend's (partner effect) co-rumination. Also, an individual's attachment anxiety was significantly related to their friend's (partner level) co-rumination. Interestingly, gender moderated the effect of attachment avoidance on co-rumination at the actor and partner levels and gender moderated the effect of attachment anxiety on corumination at the partner level. Furthermore, an interaction emerged between friendship duration and trait depression on co-rumination at the actor level. Considering the adjustment trade-offs of co-rumination, it is important to understand the predictors of corumination as well as the consequences of it in order to effectively apply intervention efforts. Thus, the findings from the current study have significant practical implications. Furthermore, evidence from this study advances previous research that has primarily gathered information from only one friend, despite the dyadic nature of the construct.