Adrenoleukodystrophy is a neurodegenerative X-linked recessive disorder. It is characterized by abnormal function of peroxisomes, which leads to an accumulation of very long-chain fatty acids in plasma and tissues, especially in the cortex of adrenal glands and white matter of the central nervous system, causing demyelinating disease and adrenocortical insufficiency (Addison's disease). It is caused by a mutation in the ABCD1 gene (ATP-binding cassette, subfamily D, member 1), which encodes the protein adrenoleukodystrophy that is involved in the transport of fatty acids into the peroxisome for degradation. Variable expression has been recognized in families of patients who have this disease. A Brazilian family from Minas Gerais State, Brazil, was studied. The proband is an adult living in Minas Gerais State, Brazil; he had adrenomyeloneuropathy, adrenocortical insufficiency and a stable cerebral form. DNA was extracted from a blood sample and was sequenced to identify the mutation. The patient's exons were cloned for confirmation. A new mutation was found in exon 5 of the ABCD1 gene (c.1430delA), as well as a single-nucleotide polymorphism in exon 6. The mutation causes a frame shift, resulting in a truncated protein with almost total absence of the ATP binding domain.