The neutrophil/lymphocyte ratio (NLR), lymphocyte/monocyte ratio (LMR), and absolute lymphocyte count/absolute monocyte count prognostic score (ALC/AMC PS) have been described as the most useful prognostic tools for patients with diffuse large B-cell lymphoma (DLBCL). We retrospectively analyzed 148 Taiwanese patients with newly diagnosed diffuse large B-cell lymphoma under rituximab (R)-CHOP-like regimens from January 2001 to December 2010 at the Tri-Service General Hospital and investigated the utility of these inexpensive tools in our patients. In a univariate analysis, the NLR, LMR, and ALC/AMC PS had significant prognostic value in our DLBCL patients (NLR: 5-year progression-free survival [PFS], P = 0.001; 5-year overall survival [OS], P = 0.007. LMR: PFS, P = 0.003; OS, P = 0.05. ALC/AMC PS: PFS, P < 0.001; OS, P < 0.001). In a separate multivariate analysis, the ALC/AMC PS appeared to interact less with the other clinical factors but retained statistical significance in the survival analysis (PFS, P = 0.023; OS, P = 0.017). The akaike information criterion (AIC) analysis produced scores of 388.773 in the NLR, 387.625 in the LMR, and 372.574 in the ALC/AMC PS. The results suggested that the ALC/AMC PS appears to be more reliable than the NLR and LMR and may provide additional prognostic information when used in conjunction with the International Prognostic Index.