Objective: To study anaphylaxis in children, using a novel method of prospective, real-time case reporting, through the Canadian Pediatric Surveillance Program (CPSP). Methods: Research Ethics Board approval was obtained. Each month from January 1, 2000, through June 30, 2001,2350 Canadian physicians reported infants, children, and adolescents with anaphylaxis to the CPSP. Adherence to the case definition was monitored. Duplicate reports were eliminated. Results: During active surveillance for 18 consecutive months, more than 700 cases of anaphylaxis were reported in patients age one month to 17 years, including one fatality. 60% of the episodes occurred in infants and children < age 6 years, 24% in 6-11-year-olds, and 16% in 12-17-year-olds. 60% of all episodes occurred in males. During 75% of all episodes, a parent was present. 81% of all episodes were triggered by foods, most commonly peanuts and tree nuts; 8% by medications; 4% by insect stings; and 2% by exercise. 31% of all episodes occurred during, or after the child's first known exposure to the trigger. In 25% of all episodes, there had been a previous reaction to the trigger. First-a-id treatment consisted of epinephrine injection in 32% of episodes, and an H-1-antihistamine in 54%. Conclusions: In this large study, using a novel method of data collection, we have defined the picture of anaphylaxis in the pediatric population.