A 2-month-old female infant, born at 25 weeks’ gestation, presented with intermittent focal bulging of the left anterior chest wall since birth, apparent only during expiration. Her neonatal course was complicated by surfactant-treated respiratory distress syndrome and congenital sepsis. She received continuous positive airway pressure starting on day 1 of life and was briefly intubated in her fourth week of life. There was no history of chest trauma or invasive chest procedures. A photograph of the chest wall during expiration (a) shows focal bulging below the nipple with normal overlying skin (arrow). Frontal chest radiograph (b) shows widening of the left fourth intercostal space with intercostal lung herniation (arrow), without rib fracture or malformation. Chest ultrasound (Supp Fig. 1) confirmed intermittent lung herniation through an absent intercostal muscle, synchronous with expiration. Findings were consistent with isolated congenital intercostal lung herniation. Given the absence of symptoms, conservative management was recommended