Chyloperitoneum following traumatic rupture of the subdiaphragmatic thoracic duct is a very rare lesion and in fact no case was found when reviewing the last five years of international literature. The authors report a case of traumatic chyloperitoneum caused by a penetrating sidearm wound in a young 19-year-old woman. Emergency exploratory laparotomy enabled the precise identification of the site of the thoracic duct lesion and to proceed to its immediate suture. At one year after the operation the patient is in good health.