Ascaris lumbricoides infection is rare among children in developed countries.Although large numbers of adult Ascaris in the small intestine can cause various abdominal symptoms,this infection remains asymptomatic until the number of worms in the intestine considerably increases in most cases.Ascaris causing bilious vomiting suggesting ileus is rare,especially in developed countries.A 6-year-old boy who lived in Japan,presented with abdominal colic,bilious vomiting at the pediatric emergency room.He appeared pale,and had no abdominal distention,tenderness,palpable abdominal mass,or findings of dehydration.He experienced bilious vomiting again during a physical examination.Laboratory tests showed mild elevation of white blood cells and C-reactive protein levels.Antigens of adenovirus,rotavirus,and norovirus were not detected from his stool,and stool culture showed normal flora.Ultrasonography showed multiple,round-shaped structures within the small intestine,and a tubular structure in a longitudinal scan of the small intestine.Capsule endoscopy showed a moving worm of Ascaris in the jejunum.Intestinal ascariasis should be considered as a cause of bilious vomiting in children,even at the emergency room in industrial countries.Ultrasound examination and capsule endoscopy are useful for diagnosis of pediatric intestinal ascariasis. Ascaris lumbricoides infection is rare among children in developed countries. Although large numbers of adult Ascaris in the small intestine can cause various abdominal symptoms, this infection remains asymptomatic until the number of worms in the intestine receptors increases in most cases. Ascaris causing bilious vomiting suggesting. A 6-year-old boy who lived in Japan, presented with abdominal colic, bilious vomiting at the pediatric emergency room. He pale, and had no abdominal distention, tenderness, palpable abdominal mass, or findings of dehydration. He experienced bilious vomiting again during a physical examination. Laboratory studies showed mild elevation of white blood cells and C-reactive protein levels. Antigens of adenovirus, rotavirus, and norovirus were not detected from his stool, and stool culture showed Normal flora. Ultrasonography showed multiple, round-shaped structures within the small intestine, and a tubular structure in a longitudinal scan of the small intestine. Capsule endoscopy showed a moving worm of Ascaris in the jejunum. Intestinal ascariasis should be considered as a cause of bilious vomiting in children, even at the emergency room in industrial countries. Ultrasound examination and capsule endoscopy are useful for diagnosis of pediatric intestinal ascariasis.