BackgroundTrauma is associated with a high morbidity and mortality, and thoracic trauma accounts for a quarter of these deaths. This is due to the penetrating thoracic trauma that often causes serious injury to the heart and great vessels. Most penetrating thoracic wounds are caused by stabbing, which is usually caused by knives. Here, we report a patient who had penetrating thoracic trauma who was caused by a knife.Case presentationA 16-year-old girl was stabbed by a knife due to an accidental fall, which caused a penetrating injury in her left chest. Despite a decreased blood pressure (100/90 mmHg), the patient was conscious. The unenhanced CT at emergency clearly showed that the knife penetrated between the pericardium and the left lung without heart injury. Exploratory thoracotomy was performed in the fourth intercostal space in combination with thoracoscopy, confirmed that the knife penetrated between the pericardium and the left lung without causing any injury to the heart.ConclusionsCT can not only clearly display foreign bodies of knives, but also accurately judge the damage of important structures such as lungs, heart and great vessels. Therefore, CT can provide information for further diagnosis and intervention.