In 2004, diabetes insipidus was the first clinical sign of Erdheim-Chester disease in our patient. Following introduction of substitution therapy with adiuretin, the patient had no further health complaints for four years until 2008 when he gradually developed dysarthria and, consequently, movement disorder in the form of mild right hemiparesis. The first CNS CT scan (2004) did not reveal any pathology. The first pathological MRI of the brain in 2006 - thickening of pituitary stalk by pathological infiltration to 4-5 mm. During the following year, further infiltrates were detected in the CNS. The number and size of CNS infiltrates increased gradually on MRIs performed repeatedly up to 2008. Erdheim-Chester disease has become suspected based on PET-CT examination at the end of 2008. CT showed irregular structure of the skeleton with noticeable sclerotic foci in otherwise osteoporotic bone structure; changes were the most evident in the long bones of lower limbs, in the pelvic bones, skull and arms, while only one vertebra was affected from within the entire spine. Finding ofthickened aortic wall (up to 8 mm) as another pathological circumstance was consistent with the Erdheim-Chester disease-associated changes described as coated aorta. CT scan revealed clear fibrotic changes in the area of retroperitoneum. Applied fluorodeoxyglucose has accumulated in the bone foci described on CTscans as well as in the thickened wall ofthe thoracic and abdominal aorta (SUV 3.6). Tc-pyrophosphonate skeleton scintigraphy showed the same bone foci as PET-CT. Full body MRI showed pathological signal from the bone marrow of the above mentioned locations, particularly during STIR imagining, where there was clear abnormal signal corresponding to accumulated histiocytes, the higher signal of which was well-differentiated from the normal bone marrow. Measurement of bone mineral density with DEXA confirmed reduced density in lumbar vertebrae to the average value of - 2.7 SD (the lowest value was -3.1SD). The disease is associated with elevated inflammatory parameters: leucocytosis, thrombocytosis, elevated CRP and fibrinogen levels. Diagnosis was verified following histological assessment ofiliac bone marrow, where focal infiltrations with foamy histiocytes of typical immunophenotype (CD68+, CD1a-, S100-) were confirmed. Treatment was initiated with chemotherapy consisting of 2g/m2 of cyclophosphamide on day 1 and 200 mg/m2 of etoposide IV infusion on days 1-3, and followed by administration of 5 microg/kg of G-CSF and collection of haematopoietic peripheral blood stem cells (PBSC). PBSC collection was followed by 5-day administration of 5 mg/m2/day of 2-chlorodeoxyadenosine (Litac) administered to the patient at monthly intervals.