Medication adherence means that patients use their drugs as recommended. There are many factors that affect medication adherence such as age, polypharmacy, patients' concerns about drug adverse effects, beliefs about medication, lack of social support, socioeconomic factors, health system, depression, lack of health literacy, communication with health care providers, and cultural considerations. Inadequate adherence to medication regimens causes worsening of disease, increases morbidity and mortality. On the other hand, nonadherence may lead to misuse of medical resources and cause serious regressions in health indicators particularly in developing countries. All over the world, one of the most substantial difficulties in health care services is ensuring patients to fully adhere to treatments. To improve adherence with treatment, there are various strategies. The evaluation of individual differences of patients is crucial for planning the treatment, hereby this approach could enhance the medication adherence of patients. The aim of this article is to review the factors leading to medication nonadherence and make recommendations to improve adherence in elderly patients.