Trisomy 21 may present with congenital chylothorax giving rise to symptoms of respiratory distress.Trisomy 21 or Down syndrome is the most common chromosome aberration in the newborn. Its high incidence has led to the better understanding of congenital diseases seen in association with this syndrome which commonly involve the cardiovascular and gastrointestinal systems. However, one of the less,if not the least, known associated condition is the pleural eusion, mostly congenital chylothorax, which is a disease characterised by lymphatic¯uid collection in the thoracic cavity of the newborn due to the leakage from the thoracic duct. We report on a newborn with trisomy 21 referred to our hospital with signs and symptoms of respiratory distress.The patient,a male newborn weighing 3,500 g at birth, was born to a 33-year-old woman gravida 3 para 3 at 39 weeks gestation by normal spontaneous vaginal delivery. He had respiratory ®ndings such as tachypnoea and cyanosis after birth and was therefore followed up for the ®rst 3 days of life after which he was discharged due to the disappearance of these symptoms. He was referred to our hospital on the 4th day of life with the same respiratory ®ndings. On admission, his body temperature was 36.7°C, pulse rate 134/min and respiratory rate 102/min. He was hypotonic and had atypical facies with low-set ears, epicanthic folds, high-arched palate and short ®ngers. Peroral cyanosis and poor breath sounds and rales were noted on the right side of the chest, together with pansystolic murmur in the mesocardiac area. The liver was 4 cm below the right costal margin.Initial laboratory ®ndings were as follows: Hb 23 g/dl, haematocrit 71%, WBC 12800/mm 3 , platelets 55000/ mm 3 , dierential blood count 52% neutrophils, 48% lymphocytes. CRP was negative. AP chest X-ray revealed a right sided pleural eusion. Thorax CT showed signi®cant pleural eusion in the right and minimal pleural eusion in the left side of the chest. ECHO showed a patent foramen ovale. Chromosome analysis revealed a 47 XY+21 karyotype. The cranial and abdominal ultrasound, TORCH screen, and thyroid hormones were all normal. Thoracentesis yielded a yellowish¯uid of pH 7.0 and density of 1010 with 6300/mm 3 leucocytes (100% lymphocytes), 90 mg/dl triglyceride, 35 mg/dl cholesterol and 2.4 g/dl protein. There were no bacteria on the gram stain and the culture was negative.Polycythaemia was treated with partial exchange transfusion. Thrombocytopenia resolved thereafter. He required two thoracenteses to relieve respiratory distress. After starting milk feeds, the yellow transparent thoracentesis¯uid became opaque and chyliform associated with increased triglycerides; therefore breast feeding was stopped and medium-chain triglyceride formula was commenced. After 6 days, the pleural eusion on the chest ®lms resolved gradually and disappeared. Breast feeding was reinitiated and the patient was discharged 14 days after the admission. He is still on breast milk and in a healthy state.The pathogenesis of congenital chylothorax is s...