Purpose: This study was to evaluate the effect of flexible bronchoscopy for the treatment of secondary atelectasis of children following respiratory infection. Methods: The medical records for a total of 19 cases of flexible bronchoscopy were reviewed retrospectively, which were performed for the treatment of secondary atelectasis at the Department of Pediatrics of the Catholic University of Korea Seoul St. Mary’s Hospital from April 2007 to January 2013. Results: A total of 18 patients (11 males and 7 females) were involved in the study. The range of age was 4 months to 15 years old. The causative underlying diseases were 17 cases of pneumonia, 1 case of bronchiolitis and 1 case of bronchial asthma. The most common location of atelectasis was right middle lobe and right middle lobe with left lower lobe was next. Bronchoscopy revealed inflammatory changes in 12 cases (63.2%) such as mucus plug (n=4), profuse secretion (n=4), mucosal edema (n=3), and bronchial narrowing (n=1), although 7 cases (36.8%) showed normal airway. Other additional findings were bronchomalacia, tracheomalacia, and bronchial tree abnormality. Seven out of 19 cases who received therapeutic intervention had complete or partial reexpansion of their atelectasis. Cases who occurred atelectasis within 6 weeks showed significantly higher improvement than cases occurred after 6 weeks (70% vs. 11.1%, P=0.019). Complications including seizure, fever, hypoxia, mucous bleeding, and hypotension were observed in 6 cases. Conclusion: Flexible bronchoscopy revealed to be effective and safe treatment modality in treatment of secondary atelectasis of children. Timely therapeutic intervention in pediatric patients should be considered. (Allergy Asthma Respir Dis 2013;1:274-279)