Non-Hodgkin's lymphomas are more unusual in pregnancy (approximately 0.8 per 100,000 pregnancies), but are usually tumors with an aggressive natural history like diffuse large B-cell lymphoma, Burkitt's lymphoma, or peripheral T-cell lymphoma. Diagnosis relies on an excisional biopsy of a tumor mass, not fine-needle aspiration. Staging evaluation is generally limited to ultrasound or MRI examinations. Diagnosis in the first trimester should prompt termination of the pregnancy followed by definitive treatment with combination chemotherapy, as aggressive lymphomas are not likely to be held at bay with single-agent chemotherapy. Women diagnosed in the second or third trimesters can be treated with standard chemotherapy, such as with cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP). The experience with rituximab in this setting is anecdotal. However, infants born of mothers who have received rituximab may have transient delay in B-cell development that typically normalizes by 6 months. The treatment outcome is similar in lymphomas diagnosed in pregnant and nonpregnant women of the same clinical stage.