Cell-of-origin (COO) classification of diffuse large B cell lymphoma (DLBCL) is increasingly important due to its prognostic significance and the development of subtype-specific therapeutics. We compared the clinical utility of the Lymph2Cx assay against four widely used immunohistochemical algorithms in 150 R-CHOP-treated DLBCL patients using archival tissue. In contrast to the predominance of germinal center B cell-like (GCB) subtype in Western populations, Lymph2Cx assay classified more than half of the Korean cases as the activated B cell-like (ABC) subtype (ABC, 83/150 [55.3%]; GCB, 51/150 [34.0%]; unclassifiable, 16/150 [10.7%]). Predominance of ABC subtype tended to be more pronounced in the nodal lymphomas than in the extranodal lymphomas. However, among the primary extranodal sites, ABC subgroups predominated in primary testicular, breast, and adrenal gland lymphomas. The classification of COO by Lymph2Cx assay did not show any significant association with clinical parameters. The overall concordance rates of the immunohistochemical algorithms with the Lymph2Cx ranged from 78.0 to 84.3%. However, 47.1-66.7% of the cases of the Lymph2Cx-defined GCB subgroup were misclassified as the non-GCB class by the IHC algorithms. The survival of Lymph2Cx-classified COO subtypes was not significantly different in the present cohort. In conclusion, ABC subtype predominated over GCB in Korean patients. There are significant discrepancies between the immunohistochemistry and Lymph2Cx classifications, especially in GCB subtype.Keywords: Asians; Cell-of-origin classification; Diffuse large B cell lymphoma; Immunohistochemistry; Lymph2Cx assay.