Sudden death due to leukostasis and lymphocyte thrombi in patients with chronic hematologic malignancies is rare. Leukostasis is characterized by highly elevated leukemic cell count and decreased tissue perfusion symptoms, leading to severe complications and even death. Chronic lymphocytic leukemia (CLL) is a chronic lymphoproliferative disorder that shows a highly heterogeneous clinical course, ranging from indolent form to very aggressive disease. Due to its low metabolic and mitotic rate, there is a lower incidence of clinically significant leukostasis in patients with CLL. Two main theories have been proposed in the development of leukostasis: (1) increased blood viscosity due to large leukemic cell populations; (2) high metabolic activity and cytokine production by leukemic cells. Both mechanisms lead to local hypoxic damage. We present a case of a 70-year-old man who died suddenly in the absence of symptoms. Autopsy and histology examinations revealed findings consistent with CLL and diffuse leukostasis involving the major organs’ vessels. In the presence of gross and/or microscopic findings suggesting a potential hematologic malignancy, undiagnosed or relapsing hematologic malignancies should be considered in the differential diagnosis of sudden deaths.