The Chernobyl disaster of 1986 is among the largest technogenic catastrophes in the history of humankind. The vast territories of Ukraine, Republic of Belarus, Russian Federation as well as bordering European states have been exposed to the contamination by the long-lived radionuclides released from the destroyed nuclear power station. The medical consequences of the Chernobyl catastrophe are being studied for more than three decades. In fact, the increased risk of certain forms of leukemia is among the major stochastic effects of radiation exposure. Nevertheless, the final unambiguous conclusions as to the role of low-dose radiation exposure in the induction of leukemia are still pending. The book presents the results of studies on the diagnosis of various forms of hematological malignancies in Ukrainian patients provided for more than thirty years in the Oncohematology Department of RE Kavetsky Institute of Experimental Pathology, Oncology and Radiobiology, the National Academy of Sciences of Ukraine. Among the groups of leukemia patients were the Chernobyl clean-up workers as well as the patients from Ukrainian population (adults and children) inhabiting the territories with different levels of radionuclide contamination. For the first time, some trends in the patterns of hematological malignancies in several sample groups under study have been identified throughout the post-Chernobyl period. The putative association between the low dose radiation exposure and the increasing risk of acute myeloid leukemia, myelodysplastic syndromes and chronic lymphocytic leukemia has been discussed based on the findings of the authors of the book as well as the data of the available literature.