Transmesenteric hernia is a rare cause of intestinal obstruction most commonly affecting the small bowel. The mesenteric defect is usually 2 to 3 cm in diameter. The authors describe 2 cases of young pediatric patients presenting with bowel obstruction resulting from a congenital mesenteric defect. The initial patient had a 30-cm-wide congenital defect in the ileal mesentery through which the sigmoid colon and some loops of small bowel had herniated. The second patient is a newborn infant who presented with symptoms and radiographic evidence of proximal bowel obstruction initially thought to be resulting from malrotation with midgut volvulus but was found at surgical exploration to have a small defect in the ileal mesentery.