This chapter presents some of the known and projected effects of exposure to ionizing nuclear radiation. Depending on the patient's radiation dose, it may be a long time, maybe hours to days, before radiation injuries manifest clinically in the patient. Of the 203 hospitalized personnel, 29 died from a combination of thermal burns and ionizing radiation injuries. The Radiation Accident Registry revealed that between 1944 and 1991 there have been at least 340 radiation accidents throughout the world involving approximately 130,000 people: 3,000 of them receiving significant exposures. A delay is probable from the time of exposure to ionizing radiation before the effects of the exposure appear clinically. Inflammation of lung tissue has apparently been caused by acute exposure to ionizing radiation. The neurovascular syndrome is the most dramatic form of acute radiation syndrome. A rapid drop in cell counts indicated acute doses in the lethal range.