Recent studies with cDNA microarrays showed that diffuse large B-cell lymphoma (DLBCL) cases with gene expression profiles similar to germinal center (GC) B cells had much better prognosis than DLBCL cases with gene expression profiles resembling activated B cells. The goal of the current study is to evaluate if using a panel of GC B-cell (CD10 and Bcl-6) and activation (MUM1/IRF4 and CD138) markers by immunohistochemistry defines prognosis in patients with de novo DLBCL. Immunohistochemical stains for the above markers were performed on paraffin-embedded tissues from 42 de novo DLBCL patients. Median follow-up in all patients was 41 months (range, 1-103 months) and in surviving patients was 65 months (range, 14-103 months). These cases could be classified into three expression patterns: GC B-cell pattern (pattern A) expressing CD10 and/or Bcl-6 but not activation markers; activated GC B-cell pattern (pattern B) expressing at least one of GC B-cell markers and one of activation markers; and activated non-GC B-cell pattern (pattern C) expressing MUM1/IRF4 and/or CD138 but not GC B-cell markers. Patients with pattern A had much better overall survival than those with the other two patterns (Kaplan-Meier survival analysis, P < 0.008, log rank test). Using multivariate Cox proportional hazards regression analysis, the international prognostic index scores and the expression pattern of these markers were independent prognostic indicators. Our results suggest that expression patterns of this panel of GC B-cell and activation markers by immunohistochemistry correlate with the prognosis of patients with DLBCL. Immunohistochemical analysis on paraffin-embedded tissues is more readily available than gene expression profiling by cDNA microarray and may provide similar prognostic information.