OBJECTIVES: Adherence to medications (AM) has been a major research priority for recent decades. Numerous factors including poor access to medicines have been identified to affect AM particularly in middle income countries (MIC). However, access to medicines seems to be addressed well in Iran as a MIC but little is known about the rate and the determinants of AM for Iranian patients. In the present study, we systematically reviewed the AM literature related to Iranian patients with diabetes (DM) and cardiovascular diseases (CVD). METHODS: We searched biomedical databases including Scopus, Web of Science, PubMed, CINAHL, and Google Scholar, Scientific Information Database, and IranMedex from inception to July 2012. Two independent researchers screened all abstracts. Studies were included if they reported rate of adherence to CVD or DM medications in Iran. We also included studies which had focused on AM determinants or AM improving interventions. Two teams of researchers reviewed full-texts of the relevant articles for quality appraisal and data extraction. We preferred qualitative synthesis of literature as the AM definitions and measurement tools were highly diverse among studies. RESULTS: Among 1003 citation, fourteen studies were eligible for review. Adherence rate for diabetic patients was 62.8-86.3% and for patients with CVD was 38.8-60.0%. Forgetfulness, lack of knowledge about medical condition and prescribed medications, and concerns about medications were consistently reported as barriers to AM. Patient education plus telephone or short message service follow-ups improved AM in diabetic patients. We found no high quality trials on AM improving interventions for patients with CVD. CONCLUSIONS: Non-adherence to medications may not be assured for accessible medicines in resource-limited settings. We strongly suggest for multidisciplinary policies and interventions on patient education and reinforcement strategies to address the issue of non-adherence to medications.