INTRODUCTION: Multiple risk factors contribute to making infection a leading cause of morbidity and mortality in oncology patients: both neoplastic disease and treatment regimens may cause disruption of mucocutaneous barriers, altered immunity, and/or viscus obstruction. The approach to a febrile oncology patient must take into consideration the nature and stage of the underlying disease, past and present treatments, any recent instrumentation or hospitalization, and any recent antibiotic exposures. EPIDEMIOLOGY: Solid malignancies can increase the risk of infection by various means. Obstruction of natural passages leads to inadequate drainage of body fluids, stasis, and increased risk of bacterial colonization and infection. In this setting, infections are typically due to organisms that are a part of the normal flora (e.g., upper respiratory tract flora causing postobstructive pneumonia, gastrointestinal flora causing postobstructive cholangitis). Solid malignancies can invade across tissue planes, leading to conduits between normally sterile areas and the external environment (e.g., rectovesicular fistulas). Central nervous system malignancies can lead to aspiration and subsequent respiratory tract infection by compromising the cough and/or swallow reflex. In addition to these secondary effects, necrotic tissue within a solid tumor itself can also be a nidus for infection. Although hematologic malignancies (lymphomas, leukemias, and plasma cell dyscrasias) are rarely associated with obstruction or with the invasion of tissue planes, they are often associated with innate, cellular and/or humoral immune system dysfunction.