Background : Although mindfulness meditation interventions have recently shown benefits for reducing stress in various populations, little is known about their relative efficacy compared with relaxation interventions. Purpose : This randomized controlled trial examines the effects of a 1-month mindfulness meditation versus somatic relaxation training as compared to a control group in 83 students (M age=25; 16 men and 67 women) reporting distress. Method : Psychological distress, positive states of mind, distractive and ruminative thoughts and behaviors, and spiritual experience were measured, while controlling for social desirability. Results : Hierarchical linear modeling reveals that both meditation and relaxation groups experienced significant decreases in distress as well as increases in positive mood states over time, compared with the control group (p<.05 in all cases). There were no significant differences between meditation and relaxation on distress and positive mood states over time. Effect sizes for distress were large for both meditation and relaxation (Cohen’s d=1.36 and .91, respectively), whereas the meditation group showed a larger effect size for positive states of mind than relaxation (Cohen’s d=.71 and .25, respectively). The meditation group also demonstrated significant pre-post decreases in both distractive and ruminative thoughts/behaviors compared with the control group (p<.04 in all cases; Cohen’s d=.57 for rumination and .25 for distraction for the meditation group), with mediation models suggesting that mindfulness meditation’s effects on reducing distress were partially mediated by reducing rumination. No significant effects were found for spiritual experience. Conclusions : The data suggest that compared with a no-treatment control, brief training in mindfulness meditation or somatic relaxation reduces distress and improves positive mood states. However, mindfulness meditation may be specific in its ability to reduce distractive and ruminative thoughts and behaviors, and this ability may provide a unique mechanism by which mindfulness meditation reduces distress.