X-linked adrenoleukodystrophy (X-ALD) is an inherited disorder of peroxisomal metabolism, biochemically characterized by deficient beta-oxidation of saturated very long chain fatty acids (VLCFA). The consequent accumulation of these fatty acids in different tissues and in biological fluids is associated with a progressive central and peripheral demyelination, as well as with adrenocortical insufficiency and hypogonadism. Seven variants of this disease have been described, cerebral childhood being the most frequent. The recommended therapy consists of the use of the glyceroltrioleate/glyceroltrierucate mixture known as Lorenzo's Oil (LO), combined with a VLCFA-poor diet, but only in asymptomatic patients will this treatment prevent the progression of the symptomatology. In the present study we evaluated the biochemical course of patients with cerebral childhood (CCER) and asymptomatic clinical forms of X-ALD treated with LO associated with a VLCFA-restricted diet. We observed that hexacosanoic acid plasma concentrations and hexacosanoic/docosanoic ratio were significantly reduced in CCER patients during treatment when compared with diagnosis. Hexacosanoic acid plasma level was significantly reduced when compared with that at diagnosis and achieved the normal levels only in asymptomatic patients under LO treatment. In asymptomatic patients the magnitude of hexacosanoic acid decrease was higher than that of the CCER patients. These results show the good biochemical response of LO treatment in asymptomatic X-ALD patients. It is possible to suppose that this could be correlated with the prevention of the appearance of neurological signals in this group of patients treated with LO.