Swyer James syndrome (SJS) is a rare disorder. It is generally discovered on a chest radiograph as increased translucency involving one hemithorax with diminished vascular markings. We present a 5-year-old girl admitted for the treatment of recurrent bronchiolitis. She was diagnosed as having Swyer James syndrome from the results of CT scan and ventilation perfusion scintigraphy, which revealed unsuspected bilateral involvement. This condition should be considered as a differential diagnosis in a patient with Swyer James (Macleod's) syndrome without an obvious etiology.