Laparoscopic pyloromyotomy has gained popularity in the treatment of hypertrophic pyloric stenosis. This is the first case report of carbon dioxide embolism during laparoscopic pyloromyotomy. We describe a case of carbon dioxide embolism in a 3-week-old neonate during laparoscopic pyloromyotomy by injection of carbon dioxide into a patent umbilical vein. The diagnosis of carbon dioxide embolism was made on the basis of the abrupt decrease in end-tidal CO(2), sudden decreased Spo(2), hypotension, and cyanosis. Portable x-ray with the clinical presentation was sufficient for a diagnosis of carbon dioxide embolism. Treatment included termination of CO(2) insufflation, placing the patient in Durant's position, and adequate resuscitation as necessary. Despite the fact that the insufflation pressure was in the recommended range, a carbon dioxide embolism was thought to be caused by injection of carbon dioxide into a patent umbilical vein. Although laparoscopic pyloromyotomy has demonstrated to be a safe and effective procedure, this is a serious and rare complication causing prolonged length of stay and skewed hospital charges.