Background/Aims: Rituximab-cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) every 14 days seems to achieve better outcomes than R-CHOP every 21 days in diffuse large B-cell lymphoma (DLBCL) patients. Currently, the standard regimen is R-CHOP every 21 days. Methods: This is a phase II clinical trial of treatment with 6 cycles of R-CHOP-14 with pegfilgrastim support in 2 populations of previously untreated DLBCL patients aged ≥65 years (n = 73) or <65 years (n = 51) with low-risk International Prognostic Index scores (0-2). Results: With a median follow-up of 63.7 months, the 5-year event-free survival rate was 53.8% in patients aged ≥65 years and 71.0% in patients aged <65 years. The 5-year overall survival rate was 71.4 and 89.8%, respectively. The complete remission rate was 69.9% for older and 80.4% for younger patients. The median relative dose intensity of cytotoxic drugs was 143.2% in the elderly and 149.1% in the young patients. Febrile neutropenia was the most common grade 3-4 adverse event, being higher in elderly patients (21.3 vs. 9.3%). Eight deaths (7 in elderly patients) were considered treatment related. Conclusion: In conclusion, the R-CHOP-14 regimen is feasible and very active, though it is more toxic in elderly patients mainly due to an increased incidence of infections. New strategies, such as new monoclonal antibodies or new targeted therapies, are needed to improve the outcomes of DLBCL patients.