A 4-year old boy was admitted to hospital with progressive respiratory failure. A chest roentgenogram revealed hyperinflated lungs and a diffuse reticular pattern. There was no smoking history in the family environment. A thin slice computed tomography of the lungs exhibited extended and diffuse cystic lung disease with no zonal predominance. An open lung biopsy showed pulmonary Langerhans cell histiocytosis. No other organs were involved. Despite treatment initiation the boy succumbed to his pulmonary insufficiency 3 weeks later. Isolated pulmonary Langerhans cell histiocytosis in children may have an unfavorable prognosis and in contrast with adults, it may present on computed tomography with lower lobe predominance and without sparing the lung bases or the anterior parts of middle lobe and lingula.