X-ray exposures to patients were measured in 50 rooms in hospitals in Ontario. For a given procedure, the total exposure for a satisfactory examination differed from one room to another by as much as a factor of 60. Skin exposures reached 90 R and more for barium enemas and barium meals, very high exposures for patients who may not be seriously ill. The factors primarily responsible for these large differences in exposure were fluoroscopic exposure rate (0.65-25 R/min) and time (0.75-12 min), kVp and filtration (8:1), choice of screen-film combination (6:1) and attenuation of table tops and phototimers (4:1). The very high exposures can readily be reduced 50% to 75% at minimal cost and without any decrease in diagnostic acceptability of the images. The use in some rooms of minimal fluoroscopic exposure rates and of 70 mm fluorography, giving total skin exposures of less than 5 R, shows that the risks from diagnostic X-rays can be made negligible with modern, properly adjusted equipment.