The paper provides the clinical and X-ray characteristics of pulmonary Langerhans cell histiocytosis (PLCH). It describes pulmonary pathohistological changes in this disease, characterizes the cellular composition of granuloma, and gives methods that can verify the diagnosis of PLCH. A case of PLCH with severe respiratory failure, for which bilateral lung transplantation and histological examination of removed lungs have been made, is described.