Objective The aim of this systematic review and meta-analysis was to assess the effectiveness of mindfulness-based stress reduction (MBSR) and mindfulness-based cognitive therapy (MBCT) in patients with breast cancer. Methods The medline, Cochrane Library, embase, cambase, and PsycInfo databases were screened through November 2011. The search strategy combined keywords for MBSR and MBCT with keywords for breast cancer. Randomized controlled trials (RCTs) comparing MBSR or MBCT with control conditions in patients with breast cancer were included. Two authors independently used the Cochrane risk of bias tool to assess risk of bias in the selected studies. Study characteristics and outcomes were extracted by two authors independently. Primary outcome measures were health-related quality of life and psychological health. If at least two studies assessing an outcome were available, standardized mean differences (SMDS) and 95% confidence intervals (CIs) were calculated for that outcome. As a measure of heterogeneity, I 2 was calculated. Results Three RCTs with a total of 327 subjects were included. One RCT compared MBSR with usual care, one RCT compared MBSR with free-choice stress management, and a three-arm RCT compared MBSR with usual care and with nutrition education. Compared with usual care, MBSR was superior in decreasing depression (SMD: -0.37; 95% CI: -0.65 to -0.08; p = 0.01; I 2 = 0%) and anxiety (SMD: -0.51; 95% CI: -0.80 to -0.21; p = 0.0009; I 2 = 0%), but not in increasing spirituality (SMD: 0.27; 95% CI: -0.37 to 0.91; p = 0.41; I 2 = 79%). Conclusions There is some evidence for the effectiveness of MBSR in improving psychological health in breast cancer patients, but more RCTs are needed to underpin those results. © 2012 Multimed Inc.