X-linked adrenoleukodystrophy is the most common peroxisomal disease among primary leukodystrophies, characterized by a progressive course and combined damage to the adrenal glands and central and peripheral nervous systems. The disease is caused by mutations in the ABCD1 gene, which encodes the ALDP transmembrane peroxisome protein, which is involved in transporting very long-chain fatty acids (VLFAs). Dysfunctions of peroxisome metabolism occur due to a lack of acyl-CoA synthetase, reducing the efficiency of beta-oxidation of VLFAs with a carbon chain length ≥C22 and resulting in the accumulation of toxic substances in the adrenal cortex and the white matter of the brain and spinal cord. We present a clinical case of X-linked adrenoleukodystrophy in a male patient with a disease onset at the age of 22 years in the form of progressive lower spastic paraparesis and neurogenic dysfunction of the pelvic organs with long-term preservation of cognitive functions. Four years after the onset of symptoms (in 2021), multiple sclerosis was clinically diagnosed. The patient received therapy with multiple sclerosis disease-modifying drugs and glucocorticosteroids. Despite treatment, disability progressed. In January 2024, a brain MRI was performed, and a diagnosis of «Leukodystrophy, Alexander’s disease?» was made. Blood serum was sent to the Research Center for Medical Genetics in Moscow under the program «Study of Genetic Heterogeneity of Leukodystrophies» for testing. In May 2024, dysphagia and apnea occurred, and after 1.5 months, the patient died outside the hospital. No necropsy was performed. Information on the course of the disease was obtained during the review of medical documentation. The diagnosis was made after the patient’s death based on the results of gas chromatography of plasma (GCP), massive parallel panel sequencing, and neuroradiological and clinical presentations. The article discusses the main MR patterns and an algorithm for diagnosing leukodystrophies.