Pulmonary lymphangioleiomyomatosis (LAM) is a rare disease of an unknown cause affecting women of reproductive age and characterised by smooth muscle proliferation along lung lymphatic channels. Pneumothorax develops in up to 80% of patients with LAM and may be the presenting manifestation of the disease. Pneumothorax also precedes or complicates the clinical course of 25% of patients with Langerhans'-cell histiocytosis (LCH, histiocytosis X) pathologically characterised by involved tissue infiltration with large numbers of unusual Langerhans' cells, often organised as granulomas. A 41-year-old female patient was treated twice by simple tube drainage due to left pneumothorax in 1996. She was then diagnosed with chronic obstructive lung disease demonstrating with dyspnea, cough and wheeze. Abnormalities found in the high-resolution computed tomography (HRCT) scanning were characteristic of LAM with thin-walled parenchymal cysts distributed homogeneously in both lungs and with thickening of interlobular septa. A 38-year-old man was hospitalised due to chronic lung failure in the course of LCH characterised by small, poorly limited nodular lesions and thin-walled cysts revealed in HRCT scans. For two years of observation, he has suffered five episodes of right pneumothorax. When diagnosing pneumothorax in the middle-age patients, the possible cause of the disease is LAM or LCH. The use of HRCT scanning may enable good determination of the nature and distribution of parenchymal abnormalities found in the diseases.