Plasmablastic lymphoma (PBL) is a rare B-cell neoplasm mostly described in human immunodeficiency virus-infected patients. Herein, we described a case of PBL presenting as gastric mass in a 21-year-old young adult without known immunodeficiency. The histological examination of the specimen showed a diffuse proliferation of round- to oval-shaped large cells with scant cytoplasm, and prominent nucleoli. The neoplasm stained positively for CD45, CD38, MUM1, and Vs38C, but typical B-cell and T-cell markers (PAX5, CD20, CD79a, and CD3) were absent. The proliferative index (Ki-67) was about 95%. And the neoplastic cells diffusely expressed the c-myc protein. Epstein-Barr virus-encoded RNA in situ hybridization was negative. Molecular genetic study via interphase fluorescence in situ hybridization disclosed the rearrangement involving c-myc gene. Awareness of this distinctive lymphoma can prevent misdiagnosis by the clinicians and/or the pathologists.