The X linked adrenoleukodystrophy (X-ALD) is a peroxisomal disease caused by defects of the ABCD1 gene on chromosome Xq28 leading to accumulation of very long chain fatty acids (VLCFA), progressive demyelination and adrenal insufficiency. An 8-year-old boy was referred to our paediatric endocrinology clinic due to fatigue and hyperpigmentation with onset at 2-years old. Blood tests revealed mineralocorticoid insufficiency. Serum adrenocorticotropic hormone and cortisol concentrations were compatible with adrenal insufficiency. Adrenal antibodies were negative. The elevated plasmatic concentration of VLCFA and the genotype analysis with sequencing of ABCD1 gene established the diagnosis of X-ALD. Brain MRI showed demyelination of white matter in the peritrigonal regions. Steroid replacement was started with good response. He initiated restriction of VLCFA by reducing the intake of fatty foods. The authors highlight the importance of suspecting of X-ALD in the aetiology of primary adrenal insufficiency as the first sign of the disease.