Patients with lysosomal storage disorders have visceral, skeletal, and neurological abnormalities and a limited life expectancy. Bone marrow transplantation has been used to correct the metabolic defects and leads to metabolic improvements in most patients However, the long-term effect of such therapy is uncertain. We analysed the data from 63 patients transplanted for lysosomal storage diseases. The transplant-related mortality was 10% if an HLA-identical sibling marrow donor was available (n=40) and 20-25% if mismatched tissue was used. Data on the effect of bone marrow transplantation on biochemical and clinical disease variables were available in 29 of the 63. 28 had a follow-up duration of 1·0-10·2 years; 1 patient died of disease progression in the first year after stable engraftment. 13 patients who had severe neurological symptoms at the time of transplantation showed disease progression. Engraftment of bone marrow in 5 patients with non-neuronopathic Gaucher's disease led to complete disappearance of symptoms. 11 patients had skeletal symptoms because of various mucopolysaccharidoses (MPSs). There was stabilisation of the skeletal lesions during the observation period of 1·4-6·4 years, but none of the patients showed significant regression of the skeletal symptoms. The visceral features (hepatosplenomegaly, cardiac hypertrophy, and upper airway obstruction) in these patients abated after transplantation. We could not evaluate the biochemical and clinical variables in 34 patients because of graft rejection, transplant-related mortality, or follow-up of less than 1 year. There were significant beneficial effects of bone marrow transplantation in patients with non-neuronopathic Gaucher's disease. Stabilisation of disease was observed in patients with MPS-I and MPS-II; this potential benefit needs to be confirmed by longer follow-up. Bone marow transplantation was not effective if severe neurological symptoms were already present at the time of transplantation.