Distressed ('Type D') personality, the combination of negative affectivity (NA) and social inhibition (SI), has been associated with adverse health outcomes. The purpose of this study was to examine if an 8-week mindfulness-based stress reduction (MBSR) program could reduce Type D personality characteristics. Distressed individuals from the Dutch general population (N = 146; mean age = 46.07; 69 % female) participated in a randomized trial comparing the mindfulness intervention with waitlist control. Although change in Type D caseness did not differ between groups, the intervention group showed stronger reductions for both NA (p < .001) and SI (p < .05) dimensions, even when change in state negative affect was statistically controlled. These effects were mediated by change in self-reported mindfulness. In conclusion, MBSR may reduce characteristics of the distressed personality type, likely through the mechanism of increased mindfulness.