Both researchers on mindfulness, as well as proponents of therapy modalities that incorporate mindfulness-based skill building, typically conceptualize the stress reducing benefits of mindfulness primarily to its ability to modulate maladaptive cognitive or attentional patterns. Naïve dialecticalism (i.e., a less synthesized and integrated tolerance of apparently contradictory or ambivalent beliefs) represents an approach to cognition that is associated with greater self-criticism and inconsistency within one's global self-concept and is thus theorized to be negatively related to mindfulness. The present study investigated whether the beneficial effects of mindfulness on cognition (i.e., lower levels of naïve dialectical thinking) are in fact accounted for via the beneficial effects of mindfulness on one's relationships (i.e., enhanced perceptions of adult attachment security). Structural equation modeling demonstrated that adult attachment security in fact fully mediated the negative relationship between naïve dialectical thinking and mindfulness. These results highlight an understanding of mindfulness meditation as a practice that cultivates not only harmonious affect and cognition, but also harmonious relationships with others.