At the Columbia-Presbyterian Medical Center, infants less than 1 year of age have a frequency of cardiac arrest during anesthesia, of 1:700, thought to be due to anesthesia, and a frequency of 1:600 attributed to anesthesia plus unknown causes. Children 1 to 12 years of age have a frequency of cardiac arrest during anesthesia of 1:2,300, thought to be due to anesthesia, and a frequency of 1:1,700 attributed to anesthesia plus unknown causes. The mortality and frequency of cardiac arrest during anesthesia in children (as defined by the number of deaths, and cardiac arrests due to anesthesia, in proportion to the incidence of anesthesia) cannot be determined in most previous reports because the total incidence of anesthesia for children was not presented. At the Columbia-Presbyterian Medical Center, the frequency of cardiac arrest during anesthesia in infants less than 1 year of age was found to be significantly higher than that in children 1 to 12 years of age or in adults 13 years of age or older. The rate for all children, infants plus children 1 to 12 years, is also significantly higher than the rate for adults. However, the rate of cardiac arrest during anesthesia in children 1 to 12 years of age was not significantly different from the rate in adults.