Despite frequent scheduled clinic contact, radiotherapy patients often seek emergency care during or shortly after their courses of treatment. Because emergency department (ED) visits add to the cost and risk of their treatment management, identifying opportunities to reduce these visits could benefit both patients and the healthcare system. We hypothesized that a subset of radiotherapy patients appropriate for nonemergent care could be identified among those using the ED. Under IRB approval, we searched our center’s electronic medical record database to identify patients who presented within 3 months of any radiation treatment from 2013 through 2016. Details of these patients’ demographics, cancer therapy, and emergency care were tabulated. Of 4,286 radiotherapy patients, 817 presented to the ED, 453 of whom were also receiving chemotherapy, and 545 of whom were being treated with curative intent. Patients were subsequently admitted 71% of the time. The highest rates of ED presentation were seen in patients with lung/thoracic cancers (30% ED use) followed by central nervous system (25%), gastrointestinal (23%), and head-and-neck (23%) cancers. Pain, electrolyte changes, neurologic symptoms, dyspnea/cough, renal dysfunction, and nausea were the most common presenting symptoms. Most patients had pain and were taking narcotic medication before the start of radiotherapy (618, 76%). A majority of subsequently admitted patients had lost weight since their diagnosis (75%), but greater weight loss was not associated with worse survival. The majority of admitted patients (87%) received, at most, intravenous therapy or a feeding tube as inpatient treatment. ED visits were most common during mid-week, and the presenting complaint typically had not been reported to the treating radiation oncologist. In this population, most patients used the ED for issues they had not reported to their oncologist and did so on days that oncology clinics are open. Pain was the most common issue and frequently preceded the start of RT. Most patients admitted through the ED received treatments that can be provided on an outpatient basis. This pattern of presentation suggests an opportunity for radiation oncologists to significantly reduce ED use among their patients during and shortly after treatment.