Leukopenia is primarily a neutropenia, and the most prominent risk of neutropenia is the susceptibility to infections, the most common sites being the skin, oral mucosa, and lungs, with the risk of infection positively correlating with the severity of neutropenia. The frequency and severity of infections varies greatly depending on the mechanism, rate and duration of neutropenia. In addition, the integrity of the skin and mucous membranes, the blood supply to the tissues, and the nutritional status of the patient determine the risk of infection. Anti-infective therapy should be instituted immediately after the onset of infection. Mild neutropenia produces infections with little or no risk of infection; however, moderate neutropenia, such as in the range of 0.5-1.0, in addition to the presence of other comorbidities only risk of infection; severe neutropenia results in the most serious infections and warrants prompt hospitalization.