We herein report the first case of a fever induced by favipiravir, a potential 
coronavirus disease 2019 therapeutic drug. An 82-year-old man diagnosed with 
bilateral pneumonia was transferred to our hospital following a positive severe 
acute respiratory syndrome coronavirus 2 polymerase chain reaction test. He was 
treated with compassionate use of favipiravir. Both his oxygen demand and fever 
gradually improved after admission; however, his fever relapsed, and the 
C-reactive protein (CRP) levels increased on day 7. We diagnosed his fever as 
being favipiravir-induced. The fever resolved a few days after favipiravir 
discontinuation, demonstrating the accuracy of the diagnosis. This case revealed 
that favipiravir can induce a fever.