A 10-year-old boy is referred to the pediatric ward for regression of school performance and behavior problems. The clinic has been evolving for two years in a context of parental separation. Given the clinical deterioration, the patient is sent to child psychiatrist. A complete somatic checkup is achieved, he reveals white matter lesions suggesting the diagnosis of X-linked adrenoleukodystrophy (X-ALD) confirmed by the metabolic assay. No curative treatment will be offered given the stage of the disease; the patient dies within two years. The X-ALD is a degenerative disease of the white matter having a prevalence estimated at 1/20,000 cases worldwide. The mutated gene, located on the long arm of chromosome X, encodes a peroxisomal membrane protein. Over 500 mutations are known and cause a disorder of fatty acids beta-oxidation. Several phenotypes exist without phenotype-genotype relationship. The diagnosis of X-ALD is mainly based on brain magnetic resonance and blood very long chain fatty acids (VLCFA) blood level. Allogenic hematopoietic stem cell transplantation, only known cure can be achieved in patients with asymptomatic (from screening) or early stage. Without treatment, the survival prognosis at diagnosis is an average of 3 years. Genetic counseling and screenings (pre-natal, neo-natal and family) are essentials to improve this diagnosis. Vigilance is crucial when dealing with child's psycho-cognitive disorders.