Langerhans cell histiocytosis (LCH) is characterized by clonal proliferation and accumulation of abnormal dendritic (Langerhans) cells in various organs. Pulmonary involvement, although rare in children, has been reported in 20%–50% of childhood cases of multisystem LCH. Isolated pulmonary LCH in children, especially in infants, is still rarer, but should be suspected in those with cystic lung disease. We report a case of a 10-month-old boy who presented with chronic dyspnea and whose chest computed tomography (CT) scan demonstrated cystic lesions. Lung biopsy established the diagnosis of LCH; microscopy revealed a background of lymphocytes and eosinophils with kidney-shaped abnormal cells. These abnormal cells were positive for S-100, CD207 (Langerin), and CD1a on immunohistochemical staining. Chemotherapy was administered using a cytotoxic agent (vinblastine) and a steroid. After 12 weeks of induction chemotherapy, although no significant change in cyst size was noted on chest CT, clinical symptoms improved. Consolidation chemotherapy was then administered for 1 year. Thereafter, chest CT findings demonstrated a significant decrease in cyst size and a significant increase in the volume of normal lung parenchyma. Therefore, aggressive treatment of isolated pulmonary LCH in infants with severe tissue destruction and symptoms seems warranted.