Purpose: This study aimed to understand the general characteristics and biomarkers of inflammation in adult patients who visited the emergency department with fever and to determine whether the severity of clinical symptoms varies according to cancer diagnosis. Methods: Data were collected retrospectively from 4,002 adult patients with fever who visited the emergency department at a tertiary hospital from January 2018 to December 2018 using medical records. Results: On average, cancer patients were older than non-cancer patients (p < .001), and differences were observed between cancer and non-cancer patients in the origin of fever and biomarkers associated with inflammation. A higher proportion of cancer patients than non-cancer patients had a Korean Triage and Acuity Scale level of 1 to 3 (p < .001), and more cancer patients than non-cancer patients met two or more criteria for systemic inflammatory response syndrome (p = .001). More life-saving interventions in the emergency department were required in cancer patients than in non-cancer patients (p < .001), and cancer patients spent more time in the emergency department than non-cancer patients (p < .001). Conclusion This study showed that the general characteristics and biomarkers of inflammation differed among adult patients with fever depending on cancer diagnosis. Furthermore, among adult patients with fever, cancer patients had more severe clinical symptoms than non-cancer patients. The results of this study are hoped to be helpful as a basis of nursing knowledge for adult patients with fever in the emergency department and as evidence for the classification of severity in patients with fever according to cancer diagnosis.