Plastic bronchitis is a rare condition in children, characterized by expectorationof branching bronchial casts. It can cause atelectasis in the lung. Herein wereported a 4.5-year-old boy with left upper lobe atelectasis due to plasticbronchitis. Although his chest X-ray is specific for left upper left atelectasis,thoracic computerized tomography had been performed and was compatiblewith obliterated left upper lobe bronchus. Typical radiological appearance ofthe left upper lobe atelectasis is not well known by clinicians which resultsunnecessary further examinations such as computerized tomography whichexposes high dose radiation. We want to emphasize the long-term side effectsof radiation and avoid unnecessary examinations in children.