단국대학교 의과대학 임상병리학과,2 단국대학교 보건과학대학 임상병리학과 C-reactive protein (CRP) levels are not generally associated with viral infections. This study investigated the changes in the CRP level caused by an infection from respiratory virus (RV). Nasopharyngeal samples from hospitalized patients with suspected RV infection were used to measure the CRP levels, virus load, virus-virus co-infection, age, sex, and length of hospital stay (LOS). Abnormal CRP levels were detected in 62.3% (3,608 out of 5,788) of all RV-positive samples. The percentage of patients with abnormal CRP levels tended to increase with age. Furthermore, LOS in patients with abnormal CRP levels was significantly longer than that in patients with normal CRP levels. The frequency of elevated CRP levels differed according to the causative virus and the frequency of abnormal levels increased with age. Moreover, LOS was longer in those with abnormal CRP levels. These data provide important insights into the role of CRP levels in RV infection.