Patient: Female, 46Final Diagnosis: Plasmablastic lymphomaSymptoms: Fecal incontinenceMedication: ChemotherapyClinical Procedure: Anal canal biopsySpecialty: Internal medicine • Oncology • RadiologyObjective:Unusual clinical courseBackground:The advent of antiretroviral therapy increased the life expectancy of human immunodeficiency virus (HIV)-positive patients and, consequently, the morbidity and mortality due to neoplasms. Plasmablastic lymphoma is one such neoplasm that generally presents with involvement of the oral cavity; cases of extra-oral involvement are rare.Case Report:We report a case of plasmablastic lymphoma in a 46-year-old woman for whom the initial clinical manifestation was a painless perineal tumor accompanied by fecal incontinence.Conclusions:The possibility of this neoplasm should be considered in patients with HIV/acquired immune deficiency syndrome (HIV/AIDS) because its early diagnosis is essential so that the start of the treatment is not delayed.