Plasmablastic lymphoma (PBL) is a rare form of diffuse large B-cell lymphoma characterized by weak/absent expression of conventional B-cell markers and strong expression of plasma cell markers. It is strongly associated with human immunodeficiency virus (HIV) and Epstein Barr virus infection, and shows an unusual tropism to the oral cavity. Herein we describe a patient with AIDS who presented with weight loss and dysphagia owing to a large gastroesophageal mass. His radiographic and endoscopic findings and long history of cigarette consumption suggested carcinoma. Biopsy demonstrated a poorly differentiated tumor stained negatively to routine lymphoid markers including CD20. However, gene rearrangement studies confirmed a B-cell process and a more detailed immunohistochemical analysis revealed the cells stained positively for CD138 (plasma cell antigen). These findings were diagnostic of PBL. Our report reviews the wide differential diagnosis of PBL and underscores the importance of a broad array of viral and molecular studies needed to establish this diagnosis.