OBJECTIVE: To determine whether financial incentives increase patients' compliance with healthcare treatments. DATA SOURCES: Systematic literature review of computer databases--Medline, Embase, PsychLit, EconLit, and the Cochrane Database of Clinical Trials. In addition, the reference list of each retrieved article was reviewed and relevant citations retrieved. STUDY SELECTION: Only randomised trials with quantitative data concerning the effect, of financial incentives (cash, vouchers, lottery tickets, or gifts) on compliance with medication, medical advice, or medical appointments were included in the review. Eleven papers were identified as meeting the selection criteria. DATA EXTRACTION: Data on study populations, interventions, and outcomes were extracted and analysed using odds ratios and the number of patients needed to be treated to improve compliance by one patient. RESULTS: 10 of the 11 studies showed improvements in patient compliance with the use of financial incentives. CONCLUSIONS: Financial incentives can improve patient compliance.