Objective—Mindfulness-based stress reduction (MBSR) is an increasingly popular practice demonstrated to alleviate stress and treat certain health conditions. MBSR may reduce elevated blood pressure (BP). Treatment guidelines recommend lifestyle modifications for BP in the prehypertensive range (SBP 120–139 or DBP 80–89), followed by antihypertensives if BP reaches hypertensive levels. MBSR has not been thoroughly evaluated as a treatment for prehypertension. A randomized clinical trial of MBSR for high BP was conducted to determine whether BP reductions associated with MBSR exceed those observed for an active control condition consisting of progressive muscle relaxation training (PMR). Methods—56 men (43%) and women (57%) averaging 50.3 (SD = 6.5) years of age (91% Caucasian) with unmedicated BP in the prehypertensive range were randomized to 8 weeks ofMBSR or PMR delivered in a group format. Treatment sessions were administered by 1 treatment provider and lasted approximately 2.5 hours each week. Clinic BP was the primary outcome measure. Ambulatory BP was a secondary outcome measure. Results—Analyses were based on intent-to-treat. Patients randomized to MBSR exhibited a 4.8 mm Hg reduction in clinic SBP, which was larger than the 0.7 mm Hg reduction observed for PMR, p = .016. Those randomized to MBSR exhibited a 1.9 mm Hg reduction in DBP, compared to a 1.2 mm Hg increase for PMR, p = .008. MBSR did not result in larger decreases in ambulatory BP than PMR. Conclusions—MBSR resulted in a reduction in clinic SBP and DBP compared to PMR.