Gastrointestinal (GI) tract perforation is one of the most severe acute abdomens. In clinical practice, abdominal x-ray plain film remains the first-line diagnostic modality for this entity. A proportion of the perforated patients, however, do not exhibit a classic x ray sign: free air at the subphrenic area. This insufficiency can bring difficulties to the diagnosis, delay appropriate treatments, and even cause lethal consequences. We describe herein a case of GI tract perforation, which was not detected by the abdominal x-ray plain film initially. Strikingly, the abdominal computed tomographic (CT)scan established the diagnosis and predicted the site and cause of the perforation, which were consistent with the intraoperative findings and pathological examination. In addition, CT scan was useful in monitoring the progression of the disease. Given the high performance of CT scan in the present case, we recommend it as a preferred diagnostic modality for patients who are suspected of GI perforation,especially when the abdominal x-ray plain film is inconclusive.