© 2014 Elsevier Inc. All rights reserved. X-linked adrenoleukodystrophy (X-ALD), is a progressive disorder of young males associated with elevated levels of very long chain fatty acids, due to defective β-oxidation and ABCD1 gene mutations encoding peroxisomal membrane protein X-ALD protein. Phenotypic variability is striking, even within a family, disease expression including asymptomatic, isolated adrenal insufficiency, adrenomyeloneuropathy (X-AMN), and X-ALD. X-ALD represents approximately 40%, X-AMN 40-45% (cerebral involvement in about one half), isolated adrenal insufficiency 10%, and a small number asymptomatic. Approximately 50% of heterozygous females develop X-AMN around the age of 40 years. Hematopoietic stem cell therapy is effective in X-ALD if initiated early, but treatment for X-AMN is lacking.