Patient: Male, 61Final Diagnosis: AITL in Klinefelter syndromeSymptoms: —Medication: —Clinical Procedure: ChemotherapySpecialty: HematologyObjective:Rare diseaseBackground:Although patients with Klinefelter syndrome have elevated risk and incidence rates for several solid cancers, reports on the incidence of hematological malignancies have been equivocal.Case Report:We report a patient diagnosed with angioimmunoblastic T-cell lymphoma in whom Klinefelter syndrome was newly detected. Moreover, we discuss the development of a variety of lymphomas in patients with Klinefelter syndrome.Conclusions:This is the first case describing angioimmunoblastic T-cell lymphoma in a patient with Klinefelter syndrome who was treated with chemotherapy.