Neonates A careful history should focus on the perinatal history, onset and duration of vomiting, nature of the vomitus, associated GI symptoms, and the presence of symptoms referable to other organ systems Onset of vomiting in the first days of life should always prompt evaluation for one of the common congenital GI anomalies that cause obstruction, such as esophageal or intestinal atresia or web, malrotation, meconium ileus, or Hirschsprung disease If the vomiting is bilious, bright yellow, or green, an urgent surgical consultation is required In most cases, a serious and possibly life-threatening mechanical obstruction may be the cause of bilious vomiting All neonates in whom the possibility of GI obstruction is entertained must have immediate flat and upright abdominal films and an upper GI series Other clinical features, such as toxicity, dehydration, and lethargy, attest to the length of time of the obstruction and its severity Except for some cases of malrotation, most neonates with a congenital basis for their bowel obstruction will present during their initial nursery stay; only rarely will the first presentation be in the ED In those rare cases where an intestinal atresia presents to the ED in the first few days of life, infants will have been vomiting since birth, evidence of obstruction with abdominal distention and bilious emesis, and plain abdominal films may show findings such as the “double bubble” of duodenal atresia Correction of dehydration and metabolic abnormalities, nasogastric decompression, and surgical consultation are the most immediate ED interventions Neonates or infants with malrotation and volvulus may present with abdominal pain (crying, drawing up their knees, poor feeding), with evidence of obstruction (bilious emesis), or an acute abdomen (abdominal distention or rigidity) Malrotation is confirmed by the abnormal radiographic location of the duodenal–jejunal junction (upper GI series) and/or the cecum (contrast enema) Immediate fluid resuscitation, GI decompression, and surgical consultation are indicated Infants with Hirschsprung disease most commonly present with delayed passage of meconium in the nursery, but may also present later with a distended abdomen and bilious vomiting Children with delayed diagnosis may also present with Hirschsprung-associated enterocolitis, with foul-smelling diarrhea, fever, and abdominal distention, or progress to life-threatening toxic megacolon Prompt recognition and treatment of electrolyte imbalance, antibiotics, and surgical consultation are essential Other serious causes of neonatal vomiting that may present to the ED include infection, such as meningitis, sepsis, pyelonephritis, omphalitis, or necrotizing enterocolitis (it should be noted that such serious infections may not be