The most common subtype of aggressive non-Hodgkin's lymphoma is diffuse large B-cell lymphoma (DLBCL). Diffuse large B-cell lymphoma represents a heterogeneous entity, with 5-year overall survival rates ranging from 26% to 73%. Microarray gene expression studies have confirmed that biologically distinct subgroups exist within DLBCL, and can be correlated with outcome. Initial management is usually guided by stage of disease at presentation. Approximately 25% of patients with DLBCL present with limited-stage disease and are treated with combined-modality therapy (brief chemotherapy and involved-field radiation). Most patients present with advanced-stage disease and require treatment with an extended course of chemotherapy. The CHOP (cyclophosphamide, doxorubicin HCl, vincristine [Oncovin], prednisone) chemotherapy regimen has been the mainstay of therapy since its development in the 1970s, as more intensive chemotherapy regimens failed to show additional benefit. The era of monoclonal antibodies has transformed treatment practices for aggressive lymphoma and has led to a significant improvement in outcome. A randomized trial comparing the use of rituximab (Rituxan), a chimeric anti-CD20 IgG1 monoclonal antibody, combined with CHOP chemotherapy vs CHOP chemotherapy alone for elderly patients with advanced-stage DLBCL demonstrated a significant benefitfor the combination approach. This finding has now been confirmed in two additional randomized, controlled trials and a population-based analysis, making CHOP and rituximab the standard of care for all newly diagnosed patients with DLBCL. Despite this advance, newer therapies are needed and many are under active investigation. The insights gained from molecular techniques such as gene expression profiling should permit identification of additional lymphoma-specific therapeutic targets and the development of novel agents that take into account underlying biology and allow for greater tailoring of therapy.