AbstractLong‐term effects of bone marrow transplantation (BMT) were evaluated in patients with I‐cell disease, metachromatic leukodystrophy (MLD), Maroteaux‐Lamy syndrome or Hunter syndrome (mild form). Donors were human leukocyte antigen (HLA)‐matched siblings, and the follow‐up periods were 24–71 months after BMT. The enzyme activities were increased in leukocytes, plasma or liver tissues compared with pre‐BMT levels. A patient with I‐cell disease acquired development of 4–8 month old infants and showed no further progression in cardiac dysfunctions. A patient with MLD showed a decelerated disease progression and an improved peripheral neuropathy, but progressive brain atrophy was not prevented. Patients with Maroteaux‐Lamy syndrome or Hunter syndrome showed improvements in hepatomegaly, joint contractures, short stature and tight skin, and this greatly increased their quality of life. These results indicated that the long‐term therapeutic effects achieved by BMT were subject to multiple factors including biochemical improvements, a reversibility of affected tissues, or advanced states of disease and central nervous system impairments in inborn