Medication adherence is a crucial part in the management of chronic diseases. As older adults form a greater proportion of the population with chronic diseases and multiple morbidities, understanding medication adherence in older adults becomes important. In the present article, we aimed to systematically review the literature for the factors associated with medication adherence in the geriatric population. We carried out a literature search using electronic databases and related keywords. 17 391 articles were reviewed in total. 65 articles were found to be relevant to our objective. A total of 80 factors of five different categories were found to be associated with medication adherence in older adults. The factors, the types of studies and the number of studies that agreed or disagreed were presented. A flower model for medication adherence was also presented to allow clinicians to better understand the complex nature of medication adherence in this population. The 80 factors reviewed were categorized into five main categories; namely, patient factors, medication factors, physician factors, system‐based factors and other factors as factors affecting poor medication adherence in older adults. Clinicians need to be mindful of the complex nature of factors affecting medication adherence in this population to optimize therapeutic outcomes. Clinicians have to be more skillful to discover and to optimize the medication adherence factors in geriatric patients. The flower model is presented as a framework for clinicians to better understand the various factors affecting medication adherence in older adults. Geriatr Gerontol Int 2016; 16: 1093–1101.