In infants with esophageal atresia (EA), lung opacities on a chest radiograph (CXR) are usually considered the cause of respiratory distress (RD). However, in some instances signs of RD and CXR changes show no correlation. The aim of this study was to investigate the pathogenesis of RD in EA patients with a normal CXR. In 41 infants with EA, CXR findings were correlated with clinical manifestations and blood-gas analysis data. The degree of abnormal gas exchange was quantitated by the arterial/alveolar oxygen tension ratio (a-ARO2). Of the 41 infants, 39(95%) presented with RD. No lung opacities were found in 130 of 294 CXRs examined (44%). An a-ARO2 below 0.75 (lower limit of normal) was calculated in 215 of 247 arterial blood samples analyzed (87%). When a temporal correlation was established, RD with a clear CXR was characterized by signs of extra- and intrathoracic airway obstruction, often associated with an a-ARO2 below 0.75. The degree of hypoxemia was greater than the degree of hypercapnia. We conclude that in infants with EA, RD with a clear CXR is related to both tracheomalacia and upper-airway obstruction that may cause miliary atelectasis not detected by conventional CXR with intrapulmonary shunting and hypoxemia.