Inflammatory myofibroblastic tumors (IMT) are rare, benign lesions. They mimic, clinically and radiologically, malignant tumors-especially sarcoma. IMT most often are seen in the lung of young adults, but there have been reports of these tumors occurring in children, in various sites. The authors report a case of appendiceal IMT arising in a 15-year-old boy previously treated for inherited distal renal tubular acidosis. He was admitted because of anorexia, weight loss, and a low-grade fever. The ultrasound study showed bilateral hydroureteronephrosis, with a poorly functioning right kidney noted on intravenous urography, and a retrovesical soft-tissue mass. Laboratory studies showed renal insufficiency, an elevated white blood cell count, anemia, thrombocytosis, and hypergammaglobulinemia. During laparotomy, a pelvic appendiceal mass was discovered, appendectomy was performed, and the pathological diagnosis of inflammatory myofibroblastic tumor was made. Three months later the boy was well, and the biological, sonographic, and urographic results had returned to normal. A review of 74 cases of abdominal IMT occurring in childhood emphasizes the importance of pathological differentiation of these lesions from malignancy, with early total excision whenever possible. Long-term follow-up is necessary to detect local recurrence, which may develop many years later, and to confirm the allegedly benign nature of these tumors.