Importance-Many people meditate to reduce psychological stress and stress-related health problems. To counsel people appropriately, clinicians need to know what the evidence says about the health benefits of meditation. Objective-To determine the efficacy of meditation programs in improving stress-related outcomes (anxiety, depression, stress/distress, positive mood, mental health quality of life, attention, substance use, eating, sleep, pain, and weight) in diverse adult clinical populations. Evidence Review-We included randomized trials with active controls that controlled for placebo effects, identified through November 2012 from MEDLINE®, PsycINFO, EMBASE®, PsycArticles, SCOPUS, CINAHL, AMED, Cochrane Library, and hand searches. Independent reviewers screened citations and extracted data. We graded the strength of evidence using four domains (risk of bias, precision, directness, and consistency) and determined the magnitude and direction of effect by calculating the relative difference between groups in change from baseline. When possible, we conducted meta-analyses using standardized mean differences to obtain aggregate estimates of effect size (ES) with 95 percent confidence intervals (CI). Findings-After reviewing 17,801 citations, we included 47 trials with 3,320 participants. Mindfulness meditation programs had moderate evidence to improve anxiety [ ES 0.38 (CI 0.12 to 0.64