Regarding the relationship between duration and causes of FUO (Table 2), 88 patients (69.8%) had FUO within 30 days, and eight patients (6.35%) had FUO for >2 months. Twenty six of 34 (76.4%) patients in the infectious disease group, 13 of 21 (61.9%) patients with malignancies, 20 of 25 (80.0%) patients in the miscellaneous group, and 20 of 30 (66.6%) patients in the undiagnosed group had a fever within 30 days, which were significantly higher than in those with a fever for >60 days (p < 0.001, p = 0.005, p < 0.001, and p < 0.001, respectively).