Background We report the first case of left pulmonary artery sling (LPAS) presenting as unilateral echogenic lung at a routine 20-week antenatal US examination. The infant had minimal symptoms at delivery, but developed an oxygen requirement and respiratory distress from day 10 of postnatal life. Antenatal US and antenatal MRI indicated an intrathoracic anomaly, so permitting definitive investigations in the neonatal period using CT, MRI and helical-CT-acquired virtual bronchoscopy. The infant successfully underwent corrective surgery.Reason to reportAntenatal ultrasound detected an anomaly permitting definitive diagnostic investigations to be performed shortly after birth. Investigations were completed before significant signs and symptoms developed.What was uniqueThis is the first report of antenatally detected unilateral echogenic lung leading to the diagnosis of pulmonary artery sling.Ramifications of this reportThis report provides further evidence that improvements in antenatal ultrasound and MRI permit earlier diagnosis and improve patient management.