There are some potential limitations to our study. First, the definition of FUO varies widely in duration from study to study. Second, the database was retrieved from only one tertiary medical center with more complicated cases, and the incidence of severe infections, malignancies, and undiagnosed cases may be higher in this hospital setting. Consequently, the results may not be able to illustrate the current epidemiology of FUO in Taiwan. In addition, some of the enrolled cases are lacking definite cultures or molecular laboratory data. In addition, diseases such as KD have not been identified in earlier studies, and the prevalence of KD varies in different regions of the world. Newly-developed diagnostic technologies can also alter the distribution of etiologies.