Mucositis, the inflammation and necrosis of mucosal membranes, is a serious and debilitating consequence of many cancer therapies. We were interested in the potential role of filgrastim (recombinant methionyl human granulocyte colony-stimulating factor, r-metHuG-CSF) in the reduction of mucositis. Patients with newly diagnosed small-cell lung cancer (SCLC) were treated with CAE chemotherapy (cyclophosphamide, doxorubicin, and etoposide) and placebo or filgrastim. If patients had an episode of febrile neutropenia, they received unblinded filgrastim in subsequent CAE cycles. Oral mucositis was considered to have occurred if a patient reported any clinical sign or symptom of oral mucositis with or without oral candidiasis. Oral mucositis was analyzed using the unadjusted chi-square test, and time to first episode of mucositis was analyzed using the stratified log-rank test as well as the Cox proportional hazards regression model. During cycle 1, placebo-treated patients had more episodes of mucositis (47%) compared with those patients randomized to filgrastim (28%). Across all cycles of treatment, 70% of placebo-treated patients experienced mucositis, compared with 53% of patients randomized to filgrastim. A significant reduction in the incidence of chemotherapy-related oral mucositis occurred across multiple cycles of treatment in patients treated with filgrastim.