Decades of research demonstrate clear bidirectional — and likely cyclical — links between depression and relationship distress; however, the precise mechanisms underlying this association remain unclear (Whisman et al., 2021). Rumination (the tendency to focus on negative thoughts and emotions in a repetitive and perseverative manner) has been studied extensively and is associated with both depression and relationship distress. Investigating this construct in an interpersonal context, however, may better elucidate the role rumination plays in both outcomes. This presentation focuses on the development and validation of the Partner Rumination Scale (PRS), a novel measure that assesses the proclivity to ruminate about a romantic partner. This instrument is comprised of 20 items (e.g., "I often have trouble letting go of negative thoughts about my partner; I think a lot about my partner's flaws"). The PRS showed excellent internal consistency (Cronbach's alpha = .95) and test-retest reliability (r = .81). Evidence of convergent and discriminant validity was demonstrated through correlations with several existing measures of rumination, an index of depressive symptom severity, and numerous instruments of relationship-related constructs. Exploratory factor analyses yielded a one-factor model that was supported via confirmatory factor analysis and cross-validated in an independent sample. Finally, the incremental validity of the PRS over two existing measures of rumination was supported in a representative sample of individuals with past depression. This study is the first to link partner rumination to depression, and the findings support the use of the PRS in both mood and relationship-specific contexts. The implications for research and practice will be discussed.