We previously developed a prognostic index, SIL, which includes advanced stage (5), soluble interleukin-2 receptor level (I), and elevated lactate dehydrogenase level (L) in diffuse large B-cell lymphoma (DLBCL) patients treated with rituximab, cyclophosphamide, hydroxydaunomycin, oncovin, and prednisone (R-CHOP). This time we evaluated the index in a larger cohort and its utility in the risk stratification. The above three factors were independent risk of progression-free survival (PFS). Five-year PFS rates in the standard-risk (SIL index: 0 or 1, n = 367) and high-risk groups (SIL index: 2 or 3, n = 205) were 79% and 53%, respectively (p < 0.0001). When the patients were divided by age (<= 60 years and >60 years), the SIL index was a good prognostic indicator for PFS in both groups as well as divided by the number of extranodal involvement site (0-1 and >1). The SIL index is a simple and objective prognostic indicator in DLBCL.