Eighteen patients with small intestine or mesenteric injury following blunt abdominal trauma were operated over a 34-month period. Early diagnosis and surgery, less than 6 hours after admission, was achieved in 10 patients (56%), seven of whom had haemorrhagic shock and had positive diagnostic peritoneal lavage or ultrasonography on admission. Three haemodynamically stable patients had a diagnostic abdominal computed tomography. Diagnosis was delayed in eight patients (44%) resulting in a gap between admission and surgery that varied from 20 hours to 46 days. The delay was related to lack of suspicion of injuries in haemodynamically stable patients despite a seat-belt sign, or false negative abdominal computed tomography. Diagnosis was delayed in six of seven patients (86%) where the only injury on admission was an isolated intestinal or mesenteric injury. In 11 patients there were associated abdominal or other system injuries. Late diagnosis was associated with an increased morbidity and longer hospital stay, relating to intestinal and mesenteric injury. In conclusion, a seat belt sign is highly suspicious of intestinal or mesenteric injury. Computed tomography was unreliable in diagnosing blunt intestinal and mesenteric injuries, and if equivocal, should be followed by diagnostic peritoneal lavage if nonoperative management is selected. Delayed diagnosis is often related to isolation of intestinal and mesenteric injury and results in increased morbidity and hospital stay. Every attempt should be made to reach a diagnosis within six hours of admission to the trauma unit. A management algorithm is proposed.