['Medical students confront significant academic, psychosocial, and existential stressors throughout their training. Mindfulness-based stress reduction (MBSR) is an educational intervention designed to improve coping skills and reduce emotional distress.', 'The purpose of this study was to examine the effectiveness of the MBSR intervention in a prospective, nonrandomized, cohort-controlled study.', 'Second-year students (n = 140) elected to participate in a 10-week MBSR seminar. Controls (n = 162) participated in a didactic seminar on complementary medicine. Profile of Mood States (POMS) was administered preintervention and postintervention.', 'Baseline total mood disturbance (TMD) was greater in the MBSR group compared with controls (38.7 +/- 33.3 vs. 28.0 +/- 31.2; p < .01). Despite this initial difference, the MBSR group scored significantly lower in TMD at the completion of the intervention period (31.8 +/- 33.8 vs. 38.6 +/- 32.8; p < .05). Significant effects were also observed on Tension-Anxiety, Confusion-Bewilderment, Fatigue-Inertia, and Vigor-Activity subscales.'] Does mindfulness-based stress reduction lower psychological distress in medical students?