BACKGROUND: The addition of rituximab to cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) chemotherapy (R-CHOP) has significantly improved clinical outcomes for patients with diffuse large B-cell lymphoma (DLBCL). However, new predictors of patient response to R-CHOP have not been established. We aimed to evaluate the impact of R-CHOP compared with CHOP in patients with DLBCL and to establish clinical predictors of better outcomes in these patients. METHODS: We retrospectively identified 177 patients diagnosed with CD20-positive DLBCL and treated with CHOP (N=82) or R-CHOP (N=95). The response rate, event-free survival (EFS), and overall survival (OS) rates were compared between the 2 treatment groups. All patients were classified into primary extranodal lymphoma (PENL) or nodal lymphoma (NL) subgroups, and the clinical parameters of each subgroup were analyzed. RESULTS: The overall response rate was higher in R-CHOP group (95% vs. 84%, P=0.07). The 3-year EFS rate was significantly higher in R-CHOP group (71% vs. 52%, P=0.013), but the OS rate was comparable between the 2 groups (79% vs. 69%, P=0.23). A significant survival benefit was seen with R-CHOP compared to CHOP therapy in NL patients (P=0.002 for EFS and 0.04 for OS). Multivariate analyses confirmed that R-CHOP therapy is an independent prognostic factor for EFS (hazard ratio of 0.32 [0.17-0.62], P=0.001) and OS (hazard ratio of 0.4 [0.18-0.87], P=0.02) in NL patients. CONCLUSION: Patients in the PENL group did not benefit from R-CHOP chemotherapy.