Four children with metachromatic leukodystrophy (MLD) underwent allogeneic bone marrow transplantation between 1988 and 1993. No effect on the natural course of the disease was observed in two children with late infantile and juvenile MLD. They had moderate neurological symptoms at the time of BMT and were followed for 7 and 6 years, respectively. The third child with the juvenile form of MLD was mildly to moderately affected when transplanted. She had lost some gross motor functions as well as speech and mental abilities at follow-up 3 years later. The fourth case, diagnosed biochemically and presymptomatically as late infantile MLD, had a subtle gait disturbance when grafted at 18 months of age. Demyelination, not observed before BMT, was visualized 1 year later on MRI. This boy's condition has continued to deteriorate 2 years after transplantation. We have adopted recent recommendations that BMT should be considered only in presymptomatic children with late infantile MLD or early in the course of juvenile MLD. In such children, still longer follow-up periods are necessary to evaluate the benefit of BMT.