The effects of bone marrow transplantation (BMT) in X-linked childhood adrenoleukodystrophy (ALD) are described in four Japanese patients. Two older patients, 10-year-old boys with IQ 60 and difficulty in school, had favourable results. IQ levels and MRI findings were generally maintained after BMT. One patient showed improvement of gait disturbance. They have both attended ordinary schools after BMT, although a learning disorder persists. On the other hand, two other younger patients with a rapid course and indeterminate IQ at BMT showed deterioration of neurological functions. Indication for BMT seems to be a maintained IQ level, preferably higher than 80, since it seems to be difficult to normalize IQ level after BMT. Younger patients have higher risk of developing a rapidly progressive form of the disease. Identification of presymptomatic boys, and serial and careful follow-up by neuropsychological and neuroradiological studies, are essential prerequisites to successful BMT in X-ALD.