Plasmablastic lymphoma (PBL) is an aggressive lymphoma commonly associated with human immunodeficiency virus (HIV) infection. Herein we describe a rare case of PBL that spontaneously regressed. An 80-year-old man was referred to our hospital owing to an exophytic gingival tumor in the right maxillary second molar region. He had no significant past medical history, and a screening test for HIV was negative. Imaging showed that the tumor measured 26 x 23 x 16 mm and was confined in the alveolar bone. The tumor was histologically comprised of highly proliferative immunoblastic cells positive for CD138 and Epstein-Barr virus (EBV)-encoded RNA. Monoclonal IgH chain gene rearrangement was detected via polymerase chain reaction. After biopsy and diagnosis of PBL, the tumor began to decrease in size and had apparently disappeared at the time of surgery. There was no histological evidence of a residual lesion in the surgical specimen. In conclusion, a minority of immunosenescence-associated PBLs in the elderly should be recognized as a unique clinicopathological entity distinct from common aggressive PBL.