IntroductionSleep disturbance is common and associated with compromised health status. Cognitive processes characterized by stress and worry can cause, or contribute to, sleep complaints. This study systematically evaluated the evidence that sleep can be improved by mindfulness-based stress reduction (MBSR), a formalized psychoeducational intervention that helps individuals self-manage and reframe worrisome and intrusive thoughts. Methods Articles were identified from searches of Medline, Allied and Complementary Medicine Database, CINAHL, PsycINFO, Digital Dissertations, and the Cochrane Central Register of Controlled Trials. Eligible for inclusion were English language clinical trials of MBSR that reported preintervention and postintervention measures of sleep quality or duration. Studies employing multicomponent interventions were excluded. Studies were reviewed independently by the first and second authors. Results Thirty-eight articles were identified for review. Seven met inclusion criteria. Lack of standardized outcome measures precluded pooling of results for quantitative data analysis. Sleep report measures varied (standardized scales, single item, sleep diaries). Four studies (all uncontrolled) found that MBSR significantly improved measures of sleep quality or duration. The remaining studies found no statistically significant difference between treatment and control conditions. Conclusions To date, controlled studies have not clearly demonstrated the positive effects of MBSR on sleep quality and duration. However, there is some evidence to suggest that increased practice of mindfulness techniques is associated with improved sleep and that MBSR participants experience a decrease in sleep-interfering cognitive processes (eg, worry). More research is needed using standardized sleep scales and methods, with particular attention to the importance of MBSR home practice.