Emergency department (ED) use for non-urgent needs is widely viewed as a contributor to various health care system flaws and inefficiencies. There are few qualitative studies designed to explore the complexity of patients' decision-making process to use the ED vs. primary care alternatives. In this study, semi-structured interviews were conducted with 30 patients who were discharged from the low acuity area of a university hospital ED. A grounded theory approach including cycles of immersion/crystallization was used to identify themes and reportable interpretations. Patients reported multiple decision-making considerations that hinged on whether or not they knew about primary care options. A model is developed depicting the complexity and variation in patients' decision-making to use the ED. Optimizing health system navigation and use requires improving objective factors such as access and costs as well as subjective perceptions of patients' health care, which are also a prominent part of their decision-making process.