Clinical data and findings of 105 cases of atelectasis in children which were confirmed by chest X-ray at Yonsei University Hospital during the period of January 1989 to December 1993 were reviewed. The result were briefly summerized as follows: 1) Atelectasis was seen most frequently below 1 year in 46 cases(43.8%) and 76 cases(72.4%) of all patients were below 5 years of age. 2) The main clinical symptom was cough in 74 cases(70.5%). The other complains were abundant expectoration in 42 cases(40%) and fever in 40 cases (38.1%). Rales were heard in 31 cases(29.5%) decreased breathing sound in 29 cases(27.6%), retraction in 20 cases(19%) and no signs in 28 cases(26.7%). 3) The involvement of the lung was usually the right upper lobe in 53 cases (50.5%) the right middle lobe in 13 cases(11.4%) and right lower lobe in 10 cases(9.5%). 4) Identifiable etiologic factors were pneumonia in 37case(35.2%) neuromuscular disease in 15 cases(14.3%), bronchiolitis in 11 cases(10.5%), asthma in 10 cases (9.5%), congenital heart disease in 10 cases(9.5%), pulmonary tuberculosis in 9 cases(8.6%), foreign body aspiration in 6 cases(5.7%), pulmonary anomaly in 5 cases(4.8%), and bronchiectasis in 2 cases(1.9%).