We investigated both pathogenesis and prevention of loop transverse stomal prolapse. Seven patients with reducible prolapsed stoma were studied under fluoroscopy after staining the prolapsed stoma and the colon by barium medium while prolapsing or reducing the stoma with or without the stomal wall pressed on to the abdominal wall of fascial plane. All prolapses occurred in the distal limbs of the loop stoma with the distal transverse colons redundant. The prolapse started around the mucocutaneous suture with the stoma inflated and the colon in it depressed and proceeded in accordance with an addition of abdominal pressure, but did not occur by pressing of the stomal wall. Prolapse of transverse loop stoma occurs when redundant colon invades the stoma with an abdominal pressure. Stomal prolapse might be prevented by fixation of the colon to the fascia.