This study was planned to investigate the characteristics of clinical and laboratory findings of patients with fever diagnosed as pulmonary embolism (PE) in comparison with PE patients without fever and patients with community-acquired pneumonia (CAP). Thirty-nine PE patients with fever without other identifiable causes (18 received antibiotics and 21 did not receive antibiotics) (study groups) were included in the study. 22 patients with PE without fever and 21 patients diagnosed with CAP were retrospectively selected as control groups. Daily peak body temperature, risk factors for PE, symptoms, and physical and laboratory findings at admission were recorded. Patients with CAP demonstrated higher body temperature than PE patients with fever (38.5 ± 0.6 versus 37.8 ± 0.6°C, P = 0.0001). Fever patterns were similar between the three groups of patients who had fever. The leukocyte count and the erythrocyte sedimentation rate (ESR) were slightly higher in the group of PE with fever versus PE without fever (11 465.6 ± 4229.4/mm 3, 51.1 ± 34.7/mm/h versus 10 777.3 ± 4927.6/mm 3, 35.2 ± 30.1/mm/h, respectively) (P > 0.05). The group of CAP showed significantly highest values of leukocyte count and ESR (15 490.5 ± 5606.3/ mm3, 69.1 ± 35.9/mm per h, respectively) (P < 0.05). This study suggested that fever might accompany with PE. The presence of slight leukocytosis and increased ESR may not securely differentiate PE patients with fever from patients with CAP. © 2005 Lippincott Williams & Wilkins.