Objective In fever clinics screening coronavirus disease (COVID-19), there could be patients with life-threatening diseases that physicians should not overlook. We exploratorily investigated the final diagnosis among non-COVID-19 hospitalized patients who visited the fever clinic. Methods This was a retrospective, observational, and single-centered study conducted in the National Center for Global Health and Medicine (NCGM), Tokyo, Japan. We conducted a retrospective chart review of patients who visited the fever clinic in the NCGM from 11 March 2020 to 24 April 2020. Patients Patients who met the following clinical criteria visited the fever clinic in the NCGM: (1) body temperature >37.5°C, (2) any symptoms consistent with COVID-19 or (3) referral from local healthcare facilities. In the fever clinic, all patients who met the above criteria had severe acute respiratory syndrome coronavirus 2 polymerase chain reaction test with nasopharyngeal swab specimens. Patients with severe symptoms or an unstable condition were sent to an outpatient clinic for infectious diseases for further evaluation and treatment. Results Among 1,470 patients who visited the fever clinic, 84 patients were hospitalized, and 45 of them were diagnosed as having COVID-19. Among the remaining 39 non-COVID-19 patients, there were nine patients with life-threatening diseases. The life-threatening diseases included acute heart failure, septic shock, pneumocystis pneumonia, peritonsillar abscess, and necrotizing fasciitis. Conclusion Physicians should evaluate each patient carefully while considering other life-threatening conditions even in such a COVID-19 pandemic era.