In the new World Health Organization/European Organization for Research and Treatment of Cancer (WHO/EORTC) classification of cutaneous lymphomas, large B-cell lymphomas (LBCLs) are divided into 3 groups: LBCL, leg-type (LBCLLT); follicle center lymphoma, diffuse type (FCLDT); and LBCL, others (LBCLO). We studied a large number of primary cutaneous LBCLs to test the validity of the classification and to identify prognostic factors for these patients. Ninety-three cases of primary cutaneous LBCL were analyzed for clinicopathologic features, expression of several markers including Bcl-2, Bcl-6, MUM-1, and FOX-P1, in situ hybridization for Epstein-Barr virus, and molecular analyses of IGH gene rearrangement and of Borrelia burgdorferi and human herpesvirus 8 DNA. Patients were classified into the following categories: FCLDT, 44 cases; LBCLLT, 40 cases; and LBCLO, 9 cases. Statistical analyses showed that the LBCLLT and FCLDT groups were clearly distinct in terms of clinicopathologic features and survival. The LBCLO group had features in between those of LBCLLT and FCLDT. Our study shows that accurate morphologic and phenotypic analyses allow us to stratify most patients into the prognostically different categories of LBCLLT and FCLDT. The definition of a third category of LBCLO requires further studies to clarify whether these cases indeed show distinct clinicopathologic features.