We report 2 cases of necrotic Meckel's diverticulum due to torsion at the neck, resulting in peritonitis. Both were young men aged 25 (Case 1) and 24 (Case 2) admitted for severe lower abdominal pain and undergoing emergency laparotomy under the diagnosis of strangulated small bowel obstruction. Meckel's diverticulum, 90×40mm in Case 1 and 100×40mm in Case 2, was found on the ileum about 100 cm proximal to Bauhin's valve in Case 1 and 75cm proximal in Case 2. It was twisted about 360°counterclockwise at the neck in Case 1 and the same degree clockwise in Case 2 and necrotic. Torsion is a rare complication of Meckel's diverticulum, and we found reports of only 2 other cases in Japan. Our 2 cases were large size of the diverticulum with ampulla at the distal end. Size, distal ampulla, and mobility may thus be an anatomical factor in such torsion.