The prognostic significance of neutropenic fever in lung cancer patients receiving chemotherapy with or without radiotherapy was investigated. Male patients and patients with squamous cell lung cancer had a higher incidence of febrile episodes than female patients and patients with other cell types, but the differences were not significant. Patients with a poor performance status had a significantly higher incidence of febrile episodes. An indwelling central venous catheter was an important risk factor for febrile episodes, indicating that bacteremia was one of the major causes of fever. The median survival time of the patients who developed febrile episodes during chemotherapy was significantly shorter than that of patients without fever (6.1 vs 12.0 months), whether or not cases of early death within 3 months were excluded (8.9 vs 13.1 months). The prevention of infectious complications during anticancer treatment by the use of rh G-CSF and the early initiation of antimicrobial chemotherapy, although the results are inconclusive, may be worthwhile.