Behcet`s disease is an inflammatory disorder characterized by recurrent oral aphthous ulcers, genital ulcers, uveitis, and skin lesions. A few cases of hematologic disease in patients with Behcet`s disease have been reported in the literature. However, acute precursor T cell lymphoblastic leukemia has never been described in association with Behcet`s disease. We recently encountered a case of acute precursor T cell lymphoblastic leukemia in a 62-year-old man with a prior diagnosis of Behcet`s disease. The patient presented with febrile neutropenia and his bone marrow biopsy revealed acute precursor T cell lymphoblastic leukemia. He was scheduled to undergo therapeutic chemotherapy, but unfortunately he died from pneumonia prior to treatment.