Ionizing radiation-induced cancer risk has been estimated mainly from the Radiation Effects Research Foundation study of atomic bomb survivors who were exposed to a high instant radiation dose. With the development of nuclear industries, the cancer risk has recently been estimated directly from epidemiological studies of radiation workers who were exposed to low-level protracted doses, though the results still remain controversial due to the lack of statistical power. The present article is to review, summarize and comment on epidemiological papers on radiation workers in various job types published up to 1994.