Eosinophilic gastroenteritis with eosinophilic infiltration of the urinary bladder wall is rare in children. We describe the CT findings of eosinophilic gastroenteritis accompanied by bladder involvement in an 11-year-old boy. CT imaging showed diffuse wall thickening of the entire gastrointestinal tract from the esophagus to the colon and revealed a halo sign, irregular fold thickening and luminal narrowing without obstruction of the gastrointestinal wall. Another CT finding was the diffuse thickening of the bladder wall with moderate enhancement on postcontrast CT. The boy underwent endoscopic biopsy from various sites of the gut wall and histology revealed increased eosinophiliac infiltration in the mucosa. After corticosteroid therapy, the boy recovered gradually. The case emphasizes that not only the gastrointestinal tract but also the urinary bladder may be involved in children with eosinophilic gastroenteritis and that recognition of CT features of this disease aids in early diagnosis and therapy.