ObjectivesMindfulness-based interventions (MBIs) have been successfully applied to persons with dementia (PwD) and their caregivers and may yield beneficial effects on depression and quality of life. However, due to inconsistent results, it may be beneficial to re-examine mindfulness in PwD cross-sectionally to identify further potential therapeutic target variables. Rumination, the maladaptive disposition to excessively think about causes and consequences of symptoms and negative mood, may represent such a target. The current study sought to confirm the validity of trait rumination and the antagonistic relationship between mindfulness, rumination, and depression in PwD and their caregivers, as this may qualify rumination as a potential process and outcome variable in future MBIs.MethodForty patients with mild dementia completed a neuropsychological examination and provided self-report data on trait mindfulness, depression, and rumination. Self-report measures were also obtained from 30 caregivers. Regression analyses were used to examine the relation between mindfulness, depression, and rumination. We used clinical cutoffs for depression and rumination to estimate the practical implications of the opposing relationships between these variables.ResultsFor PwD, mindfulness was significantly negatively correlated with depression and rumination, explaining 37% and 25% of variance, respectively. In PwD with low mindfulness scores, clinical depression and rumination syndromes occurred more frequently than in those with high mindfulness. Caregiver results were compatible.ConclusionMindfulness shows an antagonistic relationship with clinically relevant rumination in PwD. Rumination may represent a relevant clinical outcome variable for future MBIs that can be reliably measured in PwD through validated self-report measures.PreregistrationThis study is not preregistered.