question: It has generally been reported that patients with COVID-19 show a fever, cough, and/or respiratory failure as the most common clinical symptoms but some have unusual symptoms, such as anosmia, diarrhea, and throat pain. We herein report a 26-year-old woman with chief complaints of lymphadenopathy and a fever. First, she underwent a laboratory examination, which showed a high proportion of atypical lymphocytes (19%) and an increase in hepatic enzyme activities, and was then hospitalized with a diagnosis of infectious mononucleosis (IM). However, the blood examination did not show any increase in anti-Epstein-Barr virus VCM-IgM. Subsequently, she developed tonsillar hypertrophy with purulent plugs. An additional examination for infection of other pathogens revealed positivity only for SARS-CoV-2 in a loop-mediated isothermal amplification (LAMP) test. The patient was transferred to the COVID-19-specific isolation ward, and none of the ward staff, patients, or either of the two otolaryngologists who had directly examined this patient showed positive signs for SARS-CoV-2 in a LAMP test. Consequently, this case suggests that even if patients show clinical symptoms and signs of common diseases for otolaryngologists, such as IM, we should keep in mind the possibility of COVID-19 without arbitrarily assuming that IM is caused by Epstein-Barr virus.