The current research investigated whether adult attachment style moderated the effect of mindfulness-based stress reduction (MBSR) participation on levels of perceived stress. Study completing participants (secure group n = 65; insecure group n = 66) completed pre- and postintervention self-report assessments of perceived stress. The insecure group reported significantly higher stress levels prior to MBSR participation, but both groups showed significant pre–post intervention declines in perceived stress. Compared to the secure group, the insecure group also reported marginally lower perceived stress following MBSR participation. Study findings support the efficacy of MBSR for stress reduction across attachment style. Findings also suggest that MBSR participation may provide slightly greater stress reduction benefits for insecurely attached individuals.