Primary mediastinal (thymic) large B-cell lymphoma (PMBCL) is a subtype of diffuse large B-cell lymphoma (DLBCL). It commonly presents as a bulky lesion in the anterior-superior mediastinum with symptoms related to local invasion or compression. Microscopic examination typically shows infiltration of medium-large cells surrounded by collagen fibrosis. The neoplastic cells express B-cell markers, and CD30 often shows heterogeneous staining. Comparative genomic hybridization has identified gains in loci of 9p24 and 2p15 as well as Xp11.4-21 and Xq24-26. Amplification of REL and BCL11A at 2p as well as elevated expression of JAK2, PDL1, and PDL2 at 9p has been demonstrated. Nodular sclerosis classic Hodgkin lymphoma needs to be differentiated from PMBCL and cases with overlapped features have been described as mediastinal gray zone lymphoma. Primary mediastinal (thymic) large B-cell lymphoma carries a favorable prognosis in comparison to conventional DLBCL.