Meckel's diverticulitis causing pseudocyst formation in preperitoneal space has not been reported yet. A 2-year-old boy was admitted with a large lower abdominal mass. Ultrasound (US) showed a large bilobular, thick-walled, fluid-filled anechoic cystic structure with internal echos. A round radiopacity located inside of the hypodense cyst was determined on computed tomography (CT) scan. The preoperative diagnosis of this complication requires a high index of suspicion. © 2004 Elsevier Ireland Ltd. All rights reserved.