Langerhans cell histiocytosis (LCH) is a rare disease with hitherto unknown etiology and pathogenesis. It is extremely rare for clinicians to encounter histiocytic lesions of the central nervous system (CNS); the proportion of cases of which is only 1–4% of all polysystemic and multifocal bone lesions. The paper describes a clinical case of fixation amnesia in a female patient with focal brain lesions in LCH. It depicts the most characteristic clinical features and presents an algorithm for the diagnosis of histiocytic brain lesion. The results of the experimental psychological examination of the patient are considered in detail and the clinical presentations of fixation amnesia are described. There are neuroimaging data showing the lesions in the hypothalamic-pituitary region and temporal bone, which involve the auditory structures. The clinical findings have led to the conclusion that both the clinical and neuroimaging patterns of histiocytic lesions in the CNS are non-specific, which complicates the diagnostic search in LCH. For correct diagnosis and timely treatment, it is necessary to perform a biopsy of the pathological focus, followed by histological and immunohistochemical examination of the material.