Over a period of 18 years, 17 patients with proven Langerhans cell histiocytosis (LCH) were treated at the Haematological Clinic in Brno. In 13 of them, the disease was diagnosed at adult age, and 4 patients were referred to the centre with LCH diagnosed at early child age. One of these 4 patients suffered from repeated recurrences of the disease at adult age and was diagnosed with progressive neurodegenerative damage of the CNS at the age of 25 which in its terminal phase resulted in the patient's immobility, loss of sphincter control, incapacity to communicate and death at the age of 32. LCH was diagnosed at adult age in 13 patients. The form with primary bone involvement was detected in 8 out of 13 patients (62%). Only 2 of 13 patients (15%) had multiple bone lesions upon diagnosis, the remaining 6 patients (46%) had only one lesion at the time of diagnosis. Repeated recurrence of bone involvement was only recorded in 3 out of 13 patients (23%). The combination of recurrent bone involvement and the development of lung affection (dyspnoea, irritating cough, nodularities and cysts in HRCT images) were documented in 2 out of 13 patients (15%). One of the patients diagnosed with LCH at the age of37 had repeated recurrence of bone involvement, which was also treated by 2 cycles of high-dose chemotherapy and autologous transplantation. He died of bronchopneumonia due to the affection of the lungs by LCH at 48 years of age. Primary extraoseal (extamedular) involvement was diagnosed in 5 out of 13 patients (38%) (mandibular gum infiltration, single cervical node infiltration, hand skin infiltration, infiltration of the perineal region and infiltration of the hypophysial infundibular and primary lung form of LCH). In the 1st case, excision was the solution applied to the infiltration of the lingual side ofthe gums, without further recurrence. In the 2nd case, the infiltrated region of skin over the metacarpophalangeal joint was irradiated and the infiltration disappeared. In the 3rd case, the first sign ofthe disease was diabetes insipidus in a 34-year-old man, and an infiltrate in the anal region similar to condylomata acuminata. The diagnosis was confirmed 2 years after the development of diabetes insipidus from perianal infiltrates. After treatment with leustatin in 4 cycles (10 mg a day for 5 consecutive days), control MR showed that the infiltration in the hypophysial infundibular had disappeared, while the finding in the perianal region only regressed by 50% after therapy with leustatin, the reason for subsequent application of radiotherapy (20 Gy). The finding in the perianal region is normal one year after therapy, but substitution therapy with adiuretin is still necessary. The 4th patient was a case of LCH with primary pulmonary involvement diagnosed on the basis of HRCT and lavage with an immunohistochemical proof (expression of CD1 and of protein S-100) of a high number of Langerhans cells. The occurrence of LCH at adult age is rare and the disease may affect the skeleton as well as other organs. Therefore each new osteolytic lesion should be submitted for histological exam, as well as each pathologic formation, because diagnosing the disease without a microscopic and immunohistochemical exams is not possible. In the case of occurrence of diabetes insipidus at adult age, LCH should be considered as one of the possible underlying diseases. LCH pulmonary involvement should be considered in patients with an interstitial pulmonary process and the examinations should be focused accordingly (thoracoscopy with sampling for histological exams or bronchoalveolar lavage) plus the indispensable immunohistochemical examination.