Chylothorax is defined as an effusion of lymph in the pleural cavity. In the neonate both congenital and traumatic (iatrogenic) forms exist. Birth asphyxia and respiratory insufficiency are major symptoms of congenital chylothorax, requiring resuscitation and artificial ventilation. Antenatal diagnosis by ultrasound allows early therapeutic intervention such as ventilatory support and drainage of chylous fluid immediately after birth. Traumatic chylothorax is mainly seen after intrathoracic surgery. Treatment primarily consists of continuous or intermittent drainage of chyle with replacement of fluid-, electrolyte-, and protein losses and parenteral nutrition. Introduction of oral feeding is considered only after a substantial period without chyle production in the pleural cavity and consists of a medium-chain triglyceride containing formula. In a minority of cases surgical intervention is necessary.