The childhood cerebral form of X-linked adrenoleukodystrophy (X-ALD) is a severe congenital metabolic disease without a definite effective therapy except for hematopoietic stem cell transplantation in the appropriate disease stage. Seven Japanese families with X-ALD were analyzed for mutations in the ALD gene ( ALD). Of the seven families, three were referred to us for prenatal diagnosis, four for carrier detection, and three for confirmation diagnosis of patients. By nucleotide sequencing and/or restriction analysis, all the subjects to be examined were successfully diagnosed. Six different missense mutations in ALD were identified. There was a G-->A substitution (G512S) in two unrelated families, and a G-->A (R617H), a C-->T (R660W), a G-->C (R163P), a C-->T (S606L), or a G-->A (G116E) substitution in each of the other five families. Among the six substitutions, five were those reported previously and the other was a novel mutation. In three families, prenatal diagnosis was carried out after genetic counseling.