A 32-year-old man presented with severe abdominal pain located in the mesogastrium and right hemi-abdomen. A barium transit study showed a tubular structure of 6 cm arising from a bowel loop in the distal ileum, with an intraluminal polypoid mass near the bottom. Diagnosis of a benign lesion within a Meckel's diverticulum was made. Anatomopathology confirmed a Meckel's diverticulum and demonstrated that the polypoid mass was caused by an unusual great ectopic island of gastric mucosa.