Leukemia is one of the cancer sites most sensitive to the carcinogenic effect of ionizing radiation, and has the shortest latent period among radiation-induced cancers. A nested case control study of Leukemia has recently been completed in a cohort of approximately 110,000 men in Ukraine who participated in the clean-up operations following the Chornobyl accident. Leukemias and other hematological disorders have been identified from clinical records and the National Cancer Registry and confirmed by a panel of international experts. Bone marrow doses were estimated using a method called RADRUE (Radiation Dose Reconstruction with Uncertainty Estimates). Several papers have been published on leukemia risk as well as radiation dosimetry.