Prehospital care was retrospectively reviewed in 117 pulseless nonbreathing (PNB) pediatric patients (0 to 18 years of age) to determine the effects of immediate countershock treatment of asystole. Of 90 (77%) children with an initial rhythm of asystole, 49 (54%) received countershock treatment. Rhythm change occurred in ten (20%) of the asystolic children who received countershock treatment. Three of the countershocked asystolic children were successfully resuscitated, but none survived. Rhythm change occurred in nine (22%) of the asystolic children not countershocked. Six were successfully resuscitated, and one survived. The two groups (countershocked asystole v noncountershocked asystole) did not differ significantly in age, sex, witnessed arrest, witnessed arrest with bystander basic life support (BLS), prehospital endotracheal intubation, both intubation and vascular access success, or diagnosis. However, prehospital vascular access was successfully establlshed in a significantly greater number of countershocked patients (P < .05). The mean times to the scene, at the scene, and to the hospital for the countershocked v noncountershocked asystolic patients were 6.2, 23.8, and 6.1 v 5.9, 14.7 and 7.0 minutes. The mean time at the scene was significantly greater in the countershock group (P < .001). The successful performance of prehospital endotracheal intubation was significantly associated with rhythm change (P < .05). Patient's age, witnessed arrest, witnessed arrest with bystander BLS, successful establishment of prehospital vascular access, diagnosis, and countershock treatment were not significantly associated with rhythm change. In conclusion, prehospital countershock treatment prolonged prehospital care time and was not associated with rhythm change in asystolic children. Therefore, prehospital countershock treatment of asystolic children is not recommended. © 1989.