Adrenoleukodystrophy (ALD) comprises two genetically determined disorders with a different mode of inheritance, i.e., X-linked (XALD) and neonatal autosomal recessive ALD (1). Both are characterized by varying degrees of central nervous system demyelination and adrenal dysfunction as well as systemic accumulation of very long chain fatty acids (VLCFAs, fatty acids with more than 22 carbon atoms). X-linked ALD (MIM 300100) is the most common inherited peroxisomal disorder and is due to mutations or defects in the ABCD1 gene that codes for ALDP (ALD protein) (XALD) which is located in the peroxi somal membrane and functions as a crucial transporter of VLCFAs that are metabolized exclusively in peroxisomes by β-oxidation. Lacking ALDP, VLCFAs fail to enter the peroxisomes and to be activated to their coenzyme A (CoA) derivatives by VLCFA acyl-CoA synthetase (VLCS) for further catabolism (2). The mechanism of how ALDP and VLCS interact remains to be elucidated. Diagnosis relies on clinical presentation, biochemical findings of primary adrenal failure, elevated plasma level of VLCFAs, characteristic leukodystrophic changes in brain magnetic resonance imaging (MRI) and is complemented by genetic analysis. The ABCD1 gene spans about 22 kb of DNA on chromosome Xq28 and contains 10 exons. To date, more than 944 ABCD1 gene mutations have been registered in a database (http://www.x-ald.nl). We have identified a novel mutation in a Serbian family with XALD.