The prophylactic use of myeloid growth factors reduces the risk of chemotherapy-induced neutropenia and its complications, including febrile neutropenia and infection-related mortality. Perhaps most importantly, the prophylactic use of colony-stimulating factors (CSFs) has been shown to reduce the need for chemotherapy dose reductions and delays that may limit chemotherapy dose intensity, thereby increasing the potential for prolonged disease-free and overall survival in the curative setting. National surveys have shown that the majority of patients with potentially curable breast cancer or non-Hodgkin's lymphoma (NHL) do not receive prophylactic CSF support. In this issue, the National Comprehensive Cancer Network presents guidelines for the use of myeloid growth factors in patients with cancer. These guidelines recommend a balanced clinical evaluation of the potential benefits and harms associated with chemotherapy to define the treatment intention, followed by a careful assessment of the individual patient's risk for febrile neutropenia and its complications. The decision to use prophylactic CSFs is then based on the patient's risk and potential benefit from such treatment. The routine prophylactic use of CSFs in patients receiving systemic chemotherapy is recommended in patients at high risk (>20%) of developing febrile neutropenia or related complications that may compromise treatment. Where compelling clinical indications are absent, the potential for CSF prophylaxis to reduce or offset costs by preventing hospitalization for FN should be considered. The clinical, economic, and quality of life data in support of these recommendations are reviewed, and important areas of ongoing research are highlighted.