Diagnosis of diaphragmatic injury (DI) can be difficult in patients with penetrating trauma because physical examination, computed tomographic scan, chest x-ray films, and diagnostic peritoneal lavage may miss these injuries. Mandatory exploration has been recommended because of the increased mortality associated with missed DI. Thoracoscopy was prospectively evaluated as a less invasive method for diagnosing DI in patients with penetrating trauma. Over a 14-month period, 14 patients were evaluated by thoracoscopy; video thoracoscopy was used in the last 9. Findings of thoracoscopy were confirmed by laparotomy or laparoscopy. Thoracoscopy correctly identified the presence or absence of DI in nine and five patients, respectively (all patients). Video thoracoscopy was easier and faster to perform than non-video thoracoscopy. This is the first reported series in which video thoracoscopy has been used for trauma. We found this procedure to be safe, accurate, and less invasive than laparotomy for diagnosing DI.