The juvenile type of adrenoleukodystrophy is a X linked genetic disorder involving the central nervous system and the adrenal cortex. It is associated with an abnormal metabolism of saturated very long chain fatty acids. The basic defect remains unknown and there is presently no effective treatment. The authors report a familial observation which illustrates the efficacy of the techniques of identification of heterozygote females carriers and of prenatal diagnosis from trophoblast biopsy.