The report is based on one of a series of studies conducted by the United States Public Health Service to estimate population exposure from X-rays. Interest in this problem was manifested as early as 1952, and intensified in 1956, when studies were published in several countries suggesting that the levels of man-made genetically significant radiation were rather substantial. The recent passage of the Radiation Health and Safety Act of 1968 (Public Law 90-602) reflects the growing concern of responsible persons and agencies for the need for research on the effects of radiation exposure to persons and the control of radiation hazards. The X-ray Exposure Study of 1964, is providing data on the exposure and dose resulting from medical diagnostic X-ray procedures, provides an essential baseline for evaluating the effectiveness of program efforts in the control of excess radiation exposure from these procedures.