Transmesenteric hernias are extremely rare. A strangulated hernia through a mesenteric opening is a rare operative finding. Preoperative diagnosis still is difficult in spite of the imaging techniques currently available. The authors describe two cases of paediatric patients presenting with bowel obstruction resulting from a congenital mesenteric hernia. The first patient had a 3-cm wide congenital defect in the ileal mesentery through which the sigmoid colon had herniated. The second patient is a newborn infant who presented with symptoms and radiographic evidence of neonatal occlusion. At surgical exploration, a long segment of the small bowel had herniated in a defect in the ileal mesentery. A brief review of epidemiology and anatomy of transmesenteric hernias is included, along with a discussion of the difficulties in diagnosis and treatment of this condition.