The study aimed to determine the diagnostic utility of procalcitonin (PCT) in order to discriminate between infective fever and fever due to inflammation in febrile advanced lung cancer patients treated with cytotoxic chemotherapy. A total of 121 patients with advanced lung cancer, treated with a cytotoxic chemotherapy regimen between September 2007 and September 2008 at Kyoto University Hospital, were recruited. Blood samples were obtained on the first day of the fever. Serum c-reactive protein (CRP) and PCT levels were measured. At least two blood cultures were performed, and sputum was taken for Gram staining and culture. There were 71 episodes in 61 patients in the 12 months of the study, representing 50.4% of our study population. A total of 41 patients (57.7%) were diagnosed with, pneumonia using imaging modalities, 6 (8.5%) with bacteremia using blood culture and 4 (5.6%) with urinary tract infections using urine culture. Among the 41 pneumonia cases, culture from sputum revealed pathologic bacteria in 21 (51.2%) and fungal disease in 14 (34.1%) cases. Among the 71 febrile episodes, serum procalcitonin and CRP were measured in 50 episodes.. Serum procalcitonin-positive patients showed poor outcomes on antibiotics therapy (Fisher's exact test, p=0.042). Furthermore, serum procalcitonin positivity was able to discriminate infective fever from fever due to inflammation (Chi-square test, p=0.001). We showed the causative organisms of febrile advanced lung cancer patients who received cytotoxic chemotherapy, as well as the possibility of PCT to discriminate infective fever from fever due to inflammation.