Two cases of Langerhans cell histiocytosis in children of the first life year are presented. Epidemiology, pathogenesis, main clinical manifestations, principles of diagnosis, treatment, and prognosis of the disease are considered. Various clinical manifestations of histiocytosis in children lead to an inadequate assessment of the patient’s condition. Every year, from 0.5 to 10 cases are detected per 1 million of the population. Mostly children under the age of 15 are ill. Skin lesions along with damage to the skeletal system are the most common. In newborns, an isolated lesion of the skin is possible, there are no symptoms of damage to internal organs, while the general condition is not disturbed. The disease has a benign course and a favorable prognosis. The variability of skin manifestations, lesions of internal organs leads to diagnostic errors, incorrectly chosen tactics of patient management. To confirm the diagnosis, it is necessary to carry out a set of instrumental and laboratory studies including histological examination of biopsy, immunohistochemical examination of material from lesions, X-ray computed tomography to identify possible lesions of the bones and skull, as well as internal «risk organs» — lungs, spleen, kidneys, liver. Also, it is necessary to exclude the involvement of the central nervous system in the process.