The neutrophil:lymphocyte ratio (NLR) has emerged as prognostic in patients with hematological malignancies. We aimed at evaluating the NLR as predictive for complete response (CR) and prognostic for progression-free (PFS) and overall survival (OS) in a study cohort of 121 Peruvian patients with diffuse large B-cell lymphoma (DLCBL) treated with rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP). Patients with an NLR ≥6 (n = 28) were more likely to have a performance status ECOG ≥2 (74% vs. 23%; p < 0.001). NLR ≥6 was associated with lower CR rate to R-CHOP (46% vs. 74%; p = 0.02) and there was a trend towards significance in multivariate regression analyses (OR 0.36, 95% CI 0.11–1.00; p = 0.05). Patients with NLR ≥6 had lower 5-year PFS rate (39% vs. 72%; p < 0.001) and lower 5-year OS rate (46% vs. 75%; p = 0.001) than patients with NLR <6 and was an independent adverse factor for PFS (HR 2.43, 95% CI 1.21–4.87; p = 0.01) and OS (HR 2.68, 95% CI 1.31–5.47; p = 0.007) in multivariate Cox regression analyses. NLR ≥6 was prognostic of PFS and OS after adjusting for the International Prognostic Index and the NCCN-IPI scores. In conclusion, the NLR could add predictive and prognostic value to well established prognostic tools in DLBCL.