The introduction of monoclonal antibodies (MoAbs) into the treatment of cancer has led to improvements in patient survival. However, to the authors' knowledge, little attention has been paid to the infectious complications associated with their use. The authors performed a systematic review of the literature to identify randomized controlled trials (RCTs) that included in their outcomes a comparison of the infectious complications of a MoAb plus chemotherapy or radiotherapy versus the therapy regimen given without the addition of a MoAb. Twenty RCTs with relevant data regarding the use of MoAbs in patients with hematologic malignancies (10 RCTs) and solid tumors (10 RCTs) were retrieved. Six RCTs compared rituximab in conjunction with the combination of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) versus CHOP alone for the treatment of B-cell non-Hodgkin lymphoma (NHL). No significant increase in the incidence of infections was observed with the addition of rituximab to chemotherapy (based on data from 5 RCTs). However, in patients who were seropositive for the human immunodeficiency virus (HIV), a 12% increase in infection-related deaths and a rate of higher opportunistic infections was associated with the rituximab-containing regimen (data taken from 1 RCT). Five RCTs either compared trastuzumab plus chemotherapy versus chemotherapy alone or trastuzumab monotherapy versus observation in patients with breast cancer. The addition of trastuzumab to the various chemotherapy regimens was found to cause a slight increase in the frequency of high-grade infections while bevacizumab caused a negligible increase in Grade III/IV infections compared with the same regimens given of chemotherapy alone. Based on a single trial, a higher comparable increase in the rate of high-grade infections was noted with the use of cetuximab in addition to chemotherapy compared with chemotherapy alone. MoAbs added to chemotherapy appear to have infectious complications that are comparable to the chemotherapy-alone regimen when administered for the treatment of NHL, with the exception of HIV-seropositive patients. Trastuzumab, which is reported to have a clear benefit in the prognosis of breast cancer patients, was found to cause a small increase in Grade III/IV infectious complications; however, there was no apparent difference in the rate of infection-related death. Cancer 2007. © 2007 American Cancer Society.