Introduction Plasmablastic lymphoma is a rare entity that was first described in the jaws and the oral cavity of patients with human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS). Plasmablastic lymphoma is considered as a diffuse, large, B-cell lymphoma with a unique phenotype and a predilection for the oral cavity. Objectives The authors describe a case of an aggressive plasmablastic lymphoma of the oral cavity as the primary manifestation of AIDS. Resumed We report a case of plasmablastic lymphoma involving only the oral cavity as the first manifestation of AIDS. Diagnosis was confirmed by the oral lesion biopsy and the histopathologic examination that showed a dense infiltrate composed of atypical lymphocytes with numerous plasmocytes that expressed the plasma cell markers MUM-1 and CD138 and that were negative for the B-cell markers CD3, CD20, and CD45. Immunohistochemical and in situ hybridization revealed the Epstein-Barr virus genome in the atypical cells. Polymerase chain reaction was also positive for human herpesvirus-8 RNA. Conclusion The HIV serologic status should be evaluated in all patients with plasmablastic lymphoma of the oral cavity or extraoral sites.