The activation of nuclear factor kappa B (NFκB) transcription factor family is considered to have a key role in diffuse large B-cell lymphoma (DLBCL) pathogenesis and is associated with a specific molecular subtype, the activated B-cell-like (ABC) subtype. We evaluated the expression of NFκB by immunohistochemistry in a large series of DLBCL cases. The five different NFκB family members (NFκB1, NFκB2, RELA, RELB, and REL) showed a heterogeneous expression pattern with the vast majority of cases being positive for at least one factor. Two independent series of tumor samples were classified into germinal center B-cell-like (GCB) or ABC subtypes using different approaches, immunohistochemistry, or gene expression profiling, and the expression of NFκB family members was assessed. Notably, no significant differences regarding the expression of the different NFκB members were detected between the two subtypes, suggesting that NFκB signaling is a prominent feature not only in the ABC subtype, but also in the GCB tumors. Of the five transcription factors, only REL expression had a significant clinical impact on R-CHOP-treated diffuse large B-cell lymphoma, identifying a subgroup of patients with superior clinical outcome.