Background: The extent to which patients and service users are involved in medical education varies widely. There is a need for an up to date systematic review of the literature that examines what involvement (description), the potential outcome of such involvement (justification) and 'why' such involvement impacts students (clarification). Methods: Systematic searches of four databases was undertaken. Citations were screened and consensus reached for inclusion / exclusion of studies. Quality of study design and interventional presentation were assessed. Synthesis was planned at three levels-descriptive, meta-analysis and meta-ethnography, where sufficient data was available. Results: A total of 11,140 articles were initially identified, with 39 included in the review. Using the Towle Taxonomy for patient involvement in medical education we identified 4 studies that were encounter based, 17 with patients sharing their personal experiences with students, 16 with patients involved in teaching and/or evaluating students, 2 studies describing consumers as tutors and none with involvement at the institutional level. The majority (29) of studies employed outcomes at level 1 or level 2 of Kirkpatrick's hierarchy (learner reactions and modification of attitudes or skills). Outcomes in terms of benefits to learners included increased empathy and understanding of illness as experienced by patients, improved communication with patients and a greater understanding of patient-centre care. Educational quality assessment showed specific weaknesses in theoretical underpinning, curriculum outcomes, content or pedagogy. Conclusions: Patients can offer learning opportunities that are at least as effective as faculty trainers in imparting practical clinical skills and can enrich medical education by allowing learners to explore patient