Purpose: Foreign body aspiration in children is emergent and can cause serious complications. This study aims to show the clinical characteristics of foreign body aspiration and to analyze the clinical cases of delayed diagnosis to predict and prevent complica tions. Methods: We retrospectively reviewed the medical records of 63 children (48 in Inha University Hospital and 15 in Gachon Univer sity Gil Medical Center) who were diagnosed with foreign body aspiration through bronchoscopy from 1996 to 2017 in Incheon City, and analyzed clinical characteristics. Patients were divided into 3 groups: those were diagnosed within 24 hours, delayed after 24 hours, or delayed more than 7 days according to time elapse from the time of foreign body aspiration, and clinical characteristics of each group were compared. Results: Aspiration occurred in 58.7% at 1 year and 15.9% at 2 years. Cough (65.1%) and coarse breathing sound (41.3%) were most common, and radiologic findings were commonly presented as emphysema on the affected side (41.3%). Nuts were most common (42.9%), and there was no difference in the frequency between the right and left main bronchi. The documented history of foreign body aspiration was more frequently found in the early diagnosed group; however, sputum, fever, and complications were more frequent in the delayed diagnosed group. Conclusion: If a patient with respiratory disease has persistent fever or sputum, foreign body aspiration should be suspected. (Allergy Asthma Respir Dis 2018;6:303-309)