OBJECTIVES: Non-adherence to medication is one of the biggest issues in healthcare today, where roughly half of all prescriptions for drugs to be taken on an ongoing basis are either not completed or are never even filled.  Non-adherence can lead to increased rates of AEs and increased cost of care; thus, adherence to medication may impact the effectiveness of a product in the real-world.  This is especially relevant for transplant patients, where the consequences of non-adherence can increase the risk of acute rejections.  Despite this concern, information on transplant patient medication adherence is still uncommon, and a standard measure of adherence is not available.  Our objective was to examine the existing literature to assess what adherence measures are implemented and whether they are implemented routinely. METHODS: A systematic review of peer-reviewed literature was conducted to identify RCTs and observational studies that measured compliance in transplant patients taking immunosuppressive agents.  We searched Embase and Medline for studies from 2008-present in which adherence, compliance, or persistence appeared in the title, abstract, or as an index term.  RESULTS: The search identified 46 studies, of which 11 measured adherence.  Methods of measuring compliance varied among the included studies, some of which used multiple measurements:  Basel Assessment of Adherence Scale to Immunosuppressives, 2; Medication Event Monitoring System, 2; blood test, 3; self-report, 2; VAS, 1; Likert scale, 1; pill counts, 1; questionnaire, 1; continuous measures of medication adherence, 1; measure not specified in remaining studies.  In most studies, the patient, not physicians, assessed their own compliance.  CONCLUSIONS: Adherence to medication in transplant patients is neither measured regularly nor in a consistent manner.  All studies of transplant patients should assess medication adherence, and further studies must be conducted to discern a single reliable and economical measurement of compliance in transplant patients.