Background: Diaphragmatic injuries due to penetrating trauma remain a diagnostic challenge. Inspection is the best approach in diagnosis as palpation may miss some injuries. The following approaches have been used, either alone or together, to recognize penterating trauma injuries: physical examination, chest x-ray, computed tomography scan, focused assessment with sonography for trauma, and diagnostic peritoneal lavage (DPL). These modalities have been reported to miss 10 to 30 percent of injuries. These diagnostic tools have a low sensitivity and specificity to detect morbidities associated with these injuries. Finding a suitable diagnostic modality is essential for patient care. In this study, we assessed the diagnostic value of video-assisted thoracoscopy as an approach to diagnose diaphragmatic injuries in patients with negative DPL. Materials and Methods: This case series was conducted on 33 patients with penetrating thoracoabdominal trauma referred to the Loghman Hospital in Theran, Iran, from 2013 to 2014 (during an 18-month period). All negative DPL and hemodynamically stable hemopneumothorax patients with no indications for emergent surgical interventions were included in the study. All these patients underwent diagnostic thoracoscopy. Data were collected and analyzed by SPSS software version 20. Results: Thirty-three patients were eligible to participate in this study with a mean age of 23.79±6.42 years. The youngest participant was 17 years old and the oldest was 51. A penetrating wound was located in the right side in 11 patients (33.3%) and on the left side in 19 subjects (57.6%). Three patients (9.1%) had trauma on both sides of their thorax. During thoracoscopy, 6 subjects (18.2%) were found to have asymptomatic diaphragmatic injuries. Conclusions: Diaphragmatic injuries can be missed based on negative DPL. Application of video- assisted thoracoscopy is a minimally invasive procedure that is a practical approach for the evaluation, and management of trauma patients with diaphragmatic injuries