A surveillance system identified all out-of-hospital cardiac patients under the age of 18 who received emergency care in suburban King County, Washington. The etiology, cardiac rhythm, and outcome were identified for each case. During a 6 1/2-year period, 119 cardiac arrests occurred (annual incidence, 12.7/100,000 among individuals less than 18). Sudden infant death was the most common etiology (32%), and drowning was the second most common (22%). The most common rhythm was asystole, accounting for 66% of all rhythms. Six percent of patients treated with basic EMT care were discharged, compared with 7% of patients treated with EMT and paramedic care. In contrast to resuscitation from cardiac arrest in adults, the likelihood of successful resuscitation in children is very poor. This is due to different etiologies and the higher proportion of asystole seen in pediatric cardiac arrest as compared with adults.