BACKGROUND: Tremor/ataxia syndrome associated with a brittle X chromosome is a rare neurodegenerative disease. CLINICAL CASE DESCRIPTION: The article presents the clinical case of a 62 years old patient, suffering from hand tremors from the age of 5–7 with gradual onset of tremors in the head (with vocal jitter) and in the chin with further development of ataxia and mild dysarthria. After DNA-testing, the patient was diagnosed with increased levels of cytosine-guanine-guanine (CGG) trinucleotide repeats in the FMR1 gene of the Х-chromosome. Due to the absence of effect from conservative therapy and the unremitting progression of the severity of tremors, reaching the incapacitating levels, the patient underwent the stereotaxic destruction of the ventrolateral nucleus of the thalamus with focused ultrasound guided by magnetic resonance imaging (MRI) on the left side. During the process of the surgical intervention, a total of six ultrasonic exposures were delivered with achieving, based on the results of MR-thermometry, the average temperature levels of 57–60°С. The duration of treatment was 120 minutes. Right after the surgical intervention, significant clinical improvement was achieved: by 48% according to the Clinical Rating Scale for Tremor (CRST), by 80% according to the hemi-CRST (modified version of CRST for the evaluation of tremors on a single side of the body); the improvement of everyday activity according to the CRST (part С) was 87%. Thalamotomy with focused ultrasound (FUS-thalamotomy) did not cause any significant effect in this patient in terms of the aggravation of ataxia, of coordination or speech disorders. CONCLUSION: The presented clinical case demonstrates the complexity of setting the FXTAS diagnosis, as well as the necessity for the differential diagnostics of fragile Х-associated tremors and ataxia syndrome with a vast spectrum of hereditary diseases, manifesting with extrapyramidal symptoms and cognitive dysfunction. Due to the low efficiency of symptomatic medication therapy in FXTAS patients, the methods of functional neurosurgery should be considered, among which, recently more attention is gained by the MRgFUS method as the least invasive and as the safe one in the elderly individuals. As of today, the experience of performing the MRgFUS in patients with FXTAS syndrome is insignificant and contains the descriptions of single cases in foreign literature. This clinical case, the first experience of performing FUS-MRI in a patient with FXTAS syndrome in Russia, has demonstrated the potential of this approach, but further studies involving a larger number of patients and a longer observation period are certainly needed.